The sound of stress: Can noise spike your blood pressure?

SUMMARY

In their remarkable work, investigators from Baltimore, Maryland, challenged the prevailing belief that public places are less conducive to accurately measuring blood pressure (BP), given the difficulties in implementing the standards recommended by guidelines in such settings.¹ They hypothesized that BP measured in a loud public space would be higher than when measured in a quiet private space, and that using earplugs in a noisy public space (to simulate a quiet public environment) would alleviate this discrepancy. In this meticulously planned study, the investigators enrolled 108 participants from the Baltimore community through referrals, personalized mailing, and campaigning. Their mean age was 56 years; 84.3% were black, and 40.7% were women. Most had attended a chronic care clinic in the previous year, with the majority already on antihypertensive medications.

The patients were randomized into 6 groups. In each, participants underwent BP measurements in a public loud setup, a public quiet setup, and a private loud setup in different sequences. Additionally, a fourth reading was recorded in a private, quiet setting for each of the 6 groups, alongside the three sets of readings for each group. Every participant underwent 4 sets of triplicate BP measurements, with the first three in random order, followed by the fourth always in a private, quiet office, which led to 6 groups. The averages of systolic (SBP) and diastolic blood pressure (DBP) readings in public loud, public quiet, and private quiet locations were compared for differences among all groups combined, as well as in subgroups based on age, baseline hypertension, and recent healthcare utilization, using independent t-tests. The results indicated that the mean SBP measured in a public, loud space was not statistically different from that recorded in a private, quiet setup. Likewise, SBP in a public space and a private, quiet office did not differ significantly. The authors concluded that public spaces can also serve as reasonable setups for conducting a hypertension screening program, as the differences in BP readings between a loud public space and a quiet private space were not significant in this study.

COMMENT

This study challenges the common belief that noise levels affect BP measurement in public and loud places. While there is a dearth of data evaluating this concept, the available studies, like ‘Palmera,’ ‘MEPAFAR,’ and a meta-analysis, conclude that this effect may vary with study population and is primarily an incremental effect, resulting in white-coat hypertension.^2–4 Although the study re-examines this effect with a better and well-formulated novel design, objectively assessing the ambient noise level, several evident points of concern arise. First, the study enrolled participants through referrals and on personal basis. This could have resulted in selection bias, making the study population not truly representative of the general population under evaluation. Almost all patients recruited were attendees from chronic care visits, who are aware of the BP measurement procedure, which may decrease the anxiety levels and thus decrease the effect of the surroundings on the BP. Second, the study’s demographics reveal that most patients (approximately 68%) were already taking antihypertensive medications. A more detailed comparison of the study results between those on antihypertensives and those without would have been beneficial. Furthermore, an analysis among those on anti-hypertensives is warranted, comparing results between individuals with controlled and uncontrolled hypertension. Third, the study’s randomization process raises concerns due to an unequal distribution of patients in certain groups. Although sensitivity analysis using multivariate linear mixed-effects showed similar and consistent results, the lower number of patients in group 5 (following the sequence of BP readings in public loud, private quiet, public quiet, private quiet) could have resulted in interactions affecting the comparison outcomes. Moreover, the non-inclusion of heart rate at different places of measurement limits the interpretation of the effects of noise level and ambulation performed before the BP measurements.

Additionally, although this study reports no significant changes in SBP readings between different measurement settings, it does not elaborate on the dispersion of these changes. It would have been better to observe the agreement between BP readings rather than assess the changes in BP readings across different settings. The 95% limit of agreement is based on 2 times the standard deviation, whereas in the paper, 95% confidence intervals are based on the standard error of the mean. The standard deviation of the mean difference is considerable, at 8.4 mmHg, and the corresponding 95% limits of agreement would be approximately ±16.8 mmHg (the uncertainty in this estimate is due to the method used to calculate the mean difference for a Bland–Altman analysis). Given the significant variability in BP measurements between the 2 settings, it is pertinent to consider whether the authors’ interpretation of the study data remains valid. Furthermore, significant differences between DBP readings made in a public loud space and a private quiet office, and between a public quiet space and a private quiet office, should not be overlooked (p values significant for both). These findings may suggest that the effects of noise level on BP measurement, although not evident in SBP readings, could be more prominent in DBP readings. Perhaps an external validation of these findings in a larger cohort may help elucidate these differences more clearly. Lastly, the ambient noise levels (37 dB for a quiet office and 74 dB for a loud space) examined in this study were not actually representative of the noise levels seen in more congested public places and may thus inaccurately underrepresent the impact of noise levels on BP readings.

Despite the above-mentioned deficiencies, the authors have proposed and tested a novel way of assessing the effects of ambient noise levels on BP readings, paving the way for further research. A larger study planned in a similar but better design is required to unravel the true findings and settle the debate.