Abstract
Objectives
The aim of the present study was to determine whether the use of headphones to eliminate audible static during Doppler ultrasonic sphygmomanometry affects blood pressure (BP) measurement in conscious young adult (aged 1–6 years) and mature adult/senior (aged ⩾7 years) cats.
Methods
A randomized crossover study was conducted. Healthy client-owned cats (>1 year) were enrolled. Blood pressure measurements were obtained twice, 14 days apart, with or without the use of headphones worn by a veterinarian. A fear, anxiety and stress (FAS) score (0 = relaxed; 4 = severe signs) was recorded. A linear mixed-effects model was used to compare the effect of wearing headphones on BP measurement.
Results
In total, 18 young adult and 14 mature adult and senior cats with a median age of 5 years (range 1–14 years) were enrolled. Of the cats, 47% (15/32) had an average BP measurement that was at least 10 mmHg higher when not using headphones compared with using headphones, of which a majority (11/15, 73%) were young adult cats. The average BP measurement was not different when using headphones compared with when not using headphones (mean difference −7 mmHg; 95% confidence interval −14 to 0.6; P = 0.07). When compared within age groups, the average BP measurement taken when using headphones (125 ± 15 mmHg) was lower compared with the measurement taken when not using headphones (137 ± 17 mmHg) in young adult cats (P = 0.02).
Conclusions and relevance
The reduction in the average BP measurement with the use of headphones suggests this method may be helpful in reducing situational hypertension, particularly in young adult cats. Our findings also highlight the importance of consistent use of headphones when comparing serial measurements in a cat.
Introduction
Systemic hypertension is a persistent pathologic elevation in systemic arterial blood pressure (BP), with sustained elevations in systolic BP. It is a well-recognized disorder in cats, which increases in prevalence with age and disease.1,2 Pathologic hypertension can occur secondarily to disease, such as chronic kidney disease or hyperthyroidism,1,3 or medications or toxins known to cause hypertension (ie, secondary hypertension), and in the absence of an identifiable cause (ie, idiopathic hypertension).3–5 Secondary and idiopathic hypertension are diagnosed and treated only after the exclusion of a transient increase in BP from excitement, fear, stress, anxiety or in response to pain (ie, situational hypertension). 6 Failure to recognize situational hypertension can result in unnecessary life-long treatment and can potentially result in iatrogenic systemic hypotension.6,7 Equally, failure to confirm pathologic hypertension after excluding situational hypertension can result in target organ damage.6,8 Therefore, an accurate diagnosis of systemic hypertension is crucial in reducing the risk of further medical complications.
The American College of Veterinary Internal Medicine (ACVIM) and the American Association of Feline Practitioners (AAFP) developed and recently updated guidelines for appropriately collecting indirect BP measurements in conscious cats.6,7 These include the following: acclimating the patient to the room, equipment and personnel; proper patient positioning and crystal placement; using an appropriately sized cuff; and having an experienced individual collect repeated measurements.6,7 In addition, studies have evaluated the efficacy of some methods to reduce falsely high BP readings in conscious cats and found variable responses.9–14 Several effective approaches have been identified, including allowing time for cats to acclimate to the environment 9 and placing cats in their own carrier during measurement. 10
Veterinarians commonly obtain non-invasive BP measurements in cats using a Doppler ultrasonic flow detector. 15 When using the indirect Doppler technique, one potential cause of stress and fear to the patient is the audible static noise that occurs when positioning the Doppler flow probe. This noise during BP measurement could startle the cat and make it difficult to discern true pathologic hypertension from situational.12,16,17 The use of headphones by the veterinary professional to eliminate the noise during BP measurement has been recommended, although not routinely used.7,18,19 In a recent survey of veterinarians, several challenges in using Doppler were identified, with most veterinarians agreeing that this method is associated with more patient distress compared with oscillometric blood pressure devices. 15 A published abstract found that the use of headphones did not affect the BP measurements in cats. The study did not account for age, and details on practices to standardize BP measurements were minimally reported. We therefore thought it beneficial to further investigate the potential benefit of wearing headphones during Doppler BP measurements in cats using a standardized study design based on current guidelines6,7 and to also consider age as a factor.
The objective of this study was to determine whether the use of headphones during Doppler ultrasonic sphygmomanometry alters BP measurements in cats. We hypothesized that the use of headphones during measurements to eliminate audible static to the cat would lower the average BP. In the authors’ experience, the static noise startles young cats more so than older cats, and therefore a secondary objective was to determine the effect of headphones on BP by age group (young adult and mature adult/senior cats).
Materials and methods
Animals
Privately owned cats were enrolled between November 2021 and March 2022 at the Oregon State University, Carlson College of Veterinary Medicine Veterinary Teaching Hospital. Before enrolment, informed consent was obtained from the owner, along with information regarding health status, current and recent (within the past 3 months) medication history and known medical conditions. To be eligible for inclusion in the study, cats were required to be at least 1 year old. Cats with a history of chronic illness or aggressive behavior that necessitated sedation during veterinary visits, as well as those receiving medications other than flea and tick preventatives or joint supplements, were excluded from the study. Cats aged 1–6 years were categorized as young adult cats and those aged ⩾7 years were categorized as mature adult/senior cats. 20
Study design
A prospective crossover study design was used to compare the effects of eliminating noise during BP measurements with Doppler ultrasonic sphygmomanometry (Figure 1). The study was approved by the Institutional Animal Care and Use Committee (IACUC-2021-0218) at Oregon State University. The treatment order for each cat was randomized for each age group (young adult cats, mature adult/senior cats). Randomization procedures were completed using an online random assignment research randomizer (randomizer.org).
Randomized crossover study design to compare the effects of eliminating audible static during Doppler sphymomanometry
The average BP measurement was obtained twice, 14 days apart, and followed the guidelines outlined in the AAFP Hypertension Educational Toolkit. 7 A Doppler flow detector (Parks Medical Electronics) was used to measure BP, either with or without the use of headphones worn by the veterinary professional, depending on the randomization order of the cat. All measurements were performed by a single veterinarian and assisted by the same handler. Cats were brought directly into a private examination room from the parking lot, bypassing the waiting room. A feline pheromone analog diffuser (Feliway Classic Calming Diffuser; Ceva Animal Health) was used in the examination room. In the examination room, the carrier was placed on the floor. A 10-min acclimation period was provided to allow the cat to acclimate to the examination room before the BP measurement. The cat was allowed to exit the carrier before placement on an examination table with a non-skid surface, or if the top of a hard-sided carrier could be removed, the BP measurements were performed with the cat in the carrier on the examination table. A subjective fear, anxiety and stress (FAS) score was recorded at the time of BP measurement by the veterinarian performing the measurements (FAS score 0 = relaxed, 1 = subtle signs, 2–3 = moderate signs, 4 = severe signs [flight/freeze/fret], 5 = severe signs [flight/aggression]; The Spectrum of Fear, Anxiety and Stress; Fear Free). 21 The right front leg was used for the BP measurement. Cuff size was determined based on the cuff width equal to 30–40% of the limb circumference. A small portable cat friendly clipper was used to shave the fur on the palmar surface over the metacarpal artery to facilitate the identification of the pulse before the placement of the Doppler probe. The ultrasonic gel was placed on the Doppler probe and then placed on the cat over the metacarpal artery. The sound of the device was then turned on and six readings were obtained. The Doppler box was placed 1 foot away from the cat. The sound level was standardized for each measurement for all cats by the position of the dial. The measurement was performed with the cuff at approximately the same level as the heart. Minimal restraint techniques were utilized during measurements with the body position in sternal recumbency. A towel sprayed with a feline pheromone analog (Feliway Classic Calming Spray; Ceva Animal Health) was used for feline-friendly handling. 22 Before taking the measurement, the cuff was inflated and deflated twice to help the cat get used to the sensation. The cuff was slowly inflated to 20–40 mmHg above the point where blood flow was no longer heard. The first reading was excluded, and the average systolic BP was calculated using the subsequent five readings. Each cat returned 14 days later for another BP measurement performed in the same way with the same veterinary professionals according to the randomization order. The cuff size and position, restraint techniques and body position for BP measurement were recorded using the AAFP Blood Pressure Form and kept consistent between measurements.
After the BP measurement, a physical examination was performed, including axillary body temperature, respiratory rate, heart rate, body and muscle condition score, and body weight. A non-dilated indirect fundoscopy was performed after the examination.
Statistical analysis
An a priori sample size calculation (https://statulator.com/SampleSize/ss2PM.html) determined that 14 cats would achieve 80% statistical power and a level of significance of 0.05 to detect a mean difference of 10 mmHg between pairs, assuming a standard deviation of 12 mmHg. Published BP data in cats obtained by Doppler ultrasonic sphygmomanometry were used as estimates of variability. 9 Statistical analyses were performed using SAS 9.4 and Prism version 9.5.1 (GraphPad Software).
A linear mixed-effects model was developed to estimate and test the effect of wearing headphones on BP. The initial model had fixed factors of headphones, age group and an age group by headphones interaction, sex and period (ie, first vs second visit to the hospital) and sequence effects (ie, AB vs BA). There was a random intercept for each cat. The Satterthwaite degrees of freedom method and REML estimation were used. Histograms and Q-Q plots of conditional model residuals were examined and confirmed the assumption of normality. There were no period (P = 0.9), sequence (P = 0.4) or sex effects (P = 0.8); therefore, these were removed from the final model. Differences in marginal means were reported, along with a 95% confidence interval (CI). Pearson’s weighted correlation analysis was used to test for associations of BP with heart and respiratory rates and FAS scores. Based on data normality, either a paired Student’s t-test or Wilcoxon matched-pairs signed rank test was used to compare FAS score, body temperature, heart rate and respiratory rate when using headphones and without headphones. A P value <0.05 was considered significant for all analyses.
Results
A total of 32 cats were enrolled in the study with a median age of 5 years (range 1–14 years), median weight of 5.8 kg (range 2.3–8.0 kg) and sex distribution of nine spayed female cats and 23 castrated male cats. Breeds included were domestic shorthair (n = 23), British shorthair (n = 3), domestic longhair (n = 2) and Himalayan, Ragdoll, Siamese and Tonkinese (n = 1 each). Of the 32 cats, 18 were young adults with a median age of 3 years (range 1–6 years) and 14 were mature adult/senior cats with a median age of 8 years (range 7–14 years). In total, 16 cats had measurements taken using headphones first, and 16 cats had measurements taken without headphones first. All cats had a normal fundic examination.
Based on the AAFP and ACVIM hypertension guidelines, only one senior cat was found to have persistent hypertension (>160 mmHg) over the 14-day study period. Of the remaining cats, 8/31 (26%) had situational hypertension. Four of these eight cats (two adults, two seniors) had an elevated average BP measurement (>160 mmHg) only during the visit when headphones were used, and 4/8 cats (one adult, three seniors) had an elevated average BP measurement only during the visit without headphones. Many cats had an average BP measurement that was at least 10 mmHg higher (⩾10 mmHg: 15/32, 47%]; ⩾15 mmHg: 8/32, 25%; ⩾20 mmHg: 5/32, 16%) when headphones were not worn compared with when headphones were used. When cats were grouped by age, 61% (11/18), 28% (5/18) and 22% (4/18) of young adult cats and 29% (4/14), 21% (3/14) and 7% (1/14) of mature adult and senior cats had 10 mmHg, 15 mmHg and 20 mmHg higher measurements, respectively, when headphones were not worn.
The average BP measurements obtained when either using or not using headphones in cats, and specifically young adult cats and mature adult and senior cats, are summarized in Table 1 and represented in Figure 2. The average BP measurement was not different when using headphones compared with when not using headphones for all cats (P = 0.07; mean difference −7 mmHg; 95% CI −14 to 0.6) (Table 1). There was no difference in FAS score (with and without headphones: median 1, range 0–4, respectively; P = 0.4), body temperature (P = 0.4), heart rate (P = 0.5) or respiratory rate (P = 0.8) with and without headphones. There were no associations between the average BP measurement and the FAS score (r = 0.26, P = 0.2), heart rate (r = 0.33, P = 0.07) and respiratory rate (r = –0.26, P = 0.4).
Blood pressure (BP) measurements obtained by Doppler sphygmomanometry when either using or not using headphones in cats, specifically young adult cats (aged 1–6 years) and mature adult and senior cats (aged ⩾7 years)
Data are mean ± SD
Group with a statistically significant difference in BP measurement when using headphones compared with when not using headphones (P <0.05)
Dot plot of the average blood pressure measurement (mmHg) in cats obtained by Doppler sphygmomanometry using headphones (closed circle) and not using headphones (open circle) in all cats (n = 32), and specifically in young adult cats (n = 18) and mature adult and senior cats (n = 14). Lines connecting the dots signify paired samples from an individual cat
When cats were grouped by age, the average BP measurement was lower (mean difference −11 mmHg; 95% CI −1.7 to −21.1) in adult cats when using headphones compared with when not using headphones (P = 0.02). For mature adult/senior cats, the use of headphones by the veterinary professional did not affect the average BP measurement (P = 0.7) (Table 1). When evaluating all BP measurements (both with and without headphones), the average BP measurement was lower in adult cats compared with senior cats (mean difference −13 mmHg; 95% CI −3 to −23; P = 0.01).
Discussion
The present study examined the effect of audible static on the average BP measurement obtained by Doppler ultrasonic sphygmomanometry in conscious cats by comparing the measurement obtained with the veterinary professional wearing headphones or not. Contrary to our hypothesis, the use of headphones during BP measurement did not affect the average BP measurement for all cats. However, the impact of headphones on the average BP measurement varied by age group. The use of headphones was associated with significantly lower average BP in young adult cats, and no difference between methods was appreciated in senior cats. Other findings included a higher overall average BP measurement in mature adult/senior cats than young adult cats, a finding consistent with other studies.2,23,24 Contrary to other studies in dogs 25 and cats,2,14 our study did not identify any effect of sex on systolic BP.
The effect of audible static noise on BP measurements has been previously evaluated in both dogs and cats, with similar results. A study in client-owned dogs showed that only the first BP measurement was higher when taken without headphones; however, the five subsequent readings and the average of the five readings were not. 26 As previously mentioned, one published abstract with healthy and diseased client-owned cats reported no significant differences in direct Doppler flow BP measurements collected with and without headphones 8 weeks apart. 11 This is the first study that considers age to be a factor. We found that the average BP measurement was significantly lower in young adult cats when headphones were worn by the veterinary professional; however, no difference was found in mature adult/senior cats. A plausible explanation for this difference between the age groups includes reduced auditory perception with advancing age and a predisposition for younger cats to experience more stress in a hospital setting. Progressive age-related hearing loss in dogs has been demonstrated. 27 While it is likely that this can develop in cats, no clinical studies in cats have been reported to date. A previous study reported that young cats are more likely to be anxious and find a veterinary examination stressful, particularly those unfamiliar with pet carriers and car rides. 25
Previous studies have found that stress and anxiety behaviors were associated with a higher BP in dogs and cats,13,17 and stress can induce transient elevation of BP in animal models. 24 Acute stress in people increases BP by increasing cardiac output and heart rate without affecting total peripheral resistance. Furthermore, acute stress in people has been found to increase levels of catecholamines, cortisol, vasopressin, endorphins and aldosterone, which may in part explain the increase in BP.28,29 Our study did not find a significant association between BP and FAS score, and the FAS score did not differ when measurements were taken either using or not using headphones. The FAS score used in this study is a subjective scoring system based on body positions to assess fear, anxiety and stress, and does not include vocalization as one of the behavioral indicators. This scoring system has not been validated, and likely limits the detection of subtle changes in demeanor, given the narrow range of the scoring system.
The present study has some limitations. The health status of the cats was based on the owners’ self-reporting, and systemic disease, such as kidney disease or occult heart disease, cannot be excluded. Second, treatment (ie, headphones) was not blinded in this crossover study, and therefore we cannot exclude bias completely, although every effort was made to minimize this. Third, the authors chose to use only the right radial artery for BP measurements. We anticipated that our population would comprise a group of healthy cats with varying body condition scores, including some patients with a general body condition score that favored radial measurements. 30 The results of the study may not be representative of situations where the coccygeal artery is used. Finally, the 14-day interval between BP measurements was based on recommendations in the ACVIM consensus statement. The consensus statement recommends a repeat evaluation within 14 days of documentation of a BP >180 mmHg in a patient without signs of target organ damage. Our findings may not be representative of a repeat evaluation within a shorter (<14 days) or longer (>14 days) period.
Conclusions
The use of headphones during Doppler BP measurement did not result in a statistically significant difference in the average BP measurement; however, the impact of headphones was found to vary based on age group. In young adult cats, the average BP measurement taken using headphones was significantly lower than measurement taken without headphones. The reduction in the average BP measurement with the use of headphones suggests this method may be helpful in reducing situational hypertension, particularly in young adult cats. In addition, our findings highlight the importance of consistent use of headphones when comparing serial measurements in a cat.
Footnotes
Correction (October 2023):
The paper has been updated to correct a line in the Results section of the abstract: Of the cats, 47% (15/32) had an average BP measurement that was at least 10 mmHg higher when not using headphones compared with using headphones, of which a majority (11/15, 73%) were young adult cats.
Author note
An abstract was presented at the 2022 American College of Veterinary Internal Medicine Forum in Austin, TX, USA.
Conflict of interest
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: the study was funded by a donation from the Paul and Lea Levine Foundation.
Ethical approval
The work described in this manuscript involved the use of non-experimental (owned or unowned) animals. Established internationally recognised high standards (‘best practice’) of veterinary clinical care for the individual patient were always followed and/or this work involved the use of cadavers. Ethical approval from a committee was therefore not specifically required for publication in JFMS. Although not required, where ethical approval was still obtained, it is stated in the manuscript.
Informed consent
Informed consent (verbal or written) was obtained from the owner or legal custodian of all animal(s) described in this work (experimental or non-experimental animals, including cadavers) for all procedure(s) undertaken (prospective or retrospective studies). No animals or people are identifiable within this publication, and therefore additional informed consent for publication was not required.
