Respiratory Factors In Blood Pressure Regulation

Aging

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Abstract

SUMMARY OF WORK. [unreadable] [unreadable] Work during the past year has focused on the effects of guided breathing exercises on 24-hr ambulatory blood pressure in persons with prehypertension and mild hypertension, and with the mechanism by which such blood pressure effects are produced. To date, 52 candidates signed Consent Forms for this study, and began the screening process, which included in addition to a medical examination, two sessions of blood pressure monitoring in the clinic setting, and hourly recording of ambulatory blood pressure for 24-hr in their natural environments. Five of the 52 subjects were dismissed for non-cardiovascular medical or other reasons. An additional 17 candidates had either systolic (130-160mmHg) or diastolic (85-100 mmHg) blood pressures above or below the criteria for participation. The remaining 30 participants have completed the study. The target for the study is 40 subjects. [unreadable] [unreadable] The participants were assigned to either a guided breathing (GB) experimental group (n=17) or a meditative breathing (MB) control group (n=13). GB subjects were taught to use a commercially available device that detects the breathing cycle from a chest band, and presents alternating ascending and descending tones to which participants listen over earphones. Subjects are instructed to synchronize their breathing in accord with the tones, which progressively increase in duration during daily 15 min sessions to slow breathing to less than half their normal breathing rate. Participants are instructed to keep their lungs moving during the tones. The MB subjects are taught Bensonian meditative relaxation, which involves attention to the breathing cycle and silent repetition of a mantra for 15 min, with no effort to control breathing.[unreadable] [unreadable] After training, each participant engaged in a 15 min session of task breathing in the clinic setting immediately before and after one month home practice of the respective tasks. Under these conditions, breathing rate, tidal volume, minute ventilation, blood pressure, heart rate, and heart rate variability (HRV) were recorded either continuously or intermittently during 10 min baseline rest, 15 min task breathing, and 10 min recovery periods. Two sets of experimental issues are being investigated: one; what are the characteristic respiratory and cardiovascular patterns that are observed during the performance of the breathing tasks; and two, to what extent are individual differences in the antihypertensive effects of either breathing task associated with specific patterns of respiratory response during task performance?[unreadable] [unreadable] Preliminary results can be summarized as follows: during the session preceding home practice, GB decreased breathing rate (-5.3 +- 1.4 breaths/min; p < .01), and increased tidal volume (804 +-198 ml/min; p <. 01), and minute ventilation (2.6 +- 1.3; p <.05). GB decreased end tidal CO2 (-8.1 +- 1.7 mmHg (p <.01). During the recovery period after task breathing, breathing rate remained lower (3.4 +- 1.4 breaths/min) than baseline, while end tidal CO2 remained decreased from baseline (-6.9 +- 1.6 mmHg). During MB in the session preceding home practice, breathing frequency, tidal volume, minute ventilation, and end tidal CO2 were not significantly different from the baseline or recovery levels. [unreadable] [unreadable] In the clinic session after one-month of daily home practice, the characteristic patterns of breathing during task performance remained as they had been preceding home practice. For GB subjects, there was a trend for baseline breathing to be characterized by slower rate and deeper tidal volume even before task onset. No such changes in breathing pattern were observed in the MB group. [unreadable] [unreadable] Systolic blood pressure of GB subjects decreased during task performance in the clinic session both before (7.0 +- 2.1 mmHg) and after (9.9 +- 2.7 mmHg) home practice. During recovery following task performance, blood pressure of GB subjects returned to pre-task levels. No such effects were observed in the MB group during task breathing preceding home practice, but after one month home practice, MB in the clinic did decrease systolic BP acutely (4.0 +- 1.5 mmHg). Neither group showed task-induced changes in diastolic pressure. Heart rate changed by less than 2 bpm during task breathing in both groups.[unreadable] [unreadable] The effects of one month daily practice have been analyzed for 10 subjects in each group who were fully adherent to the daily regimen, as revealed by diary and automated recordings. Eight of 10 GB subjects showed lower 24-hr systolic pressure (-3.6 +- 1.6 mmHg; p <.05) and 7 of 10 showed lower 24-hr diastolic pressure (-2.6/1.2 mmHg; p <.05) after one month home practice than before. No such effects were observed in 24-hr heart rate. For MB subjects, no significant differences in 24-hr blood pressure or heart rate before and after home practice were observed. Although the magnitude of the antihypertensive effects observed to date is smaller than those reported in the literature, it is also the case that pre-intervention blood pressure levels of these subjects were lower than in previous published trials. Effects of guided breathing on HRV, Perceived Stress, and 24-hr urinary excretion of a sodium pump inhibitor that is responsive to changes in plasma volume are also being investigated in this study. The preliminary findings are consistent with the view that the salutary effects of guided breathing may be mediated, at least in part, by improved ventilation, and corresponding changes in blood gases that are relevant to renal sodium regulation. The study is continuing.