Effect of breathing instruction on blood pressure responses during isometric exercise.

Effect of Breathing Instruction on Blood Pressure Responses During Isometric Exercise Physical therapists generally use isometric exercises (ie, static contractions) to maintain muscle strength when an individual's condition precludes isotonic (dynamic) exercises. [1] It is well documented that isometric exercises are associated with an increase in blood pressure. For this reason, some health care professionals question the safety of isometric exercises, particularly in hypertensive individuals. [2-4] Recent studies have documented cases of brain stem injury and subarachnoid hemorrhage with maximal resistive exercise. [5,6] Vascular complications during isometric efforts are of great concern, especially when working with elderly patients.

Physiological mechanisms regulating the pressor responses to isometric exercise probably involve both central and peripheral control. [7,8] The peripheral mechanisms act reflexively, sending afferent impulses from the working muscles to cardiovascular centers in the brain, while impulses originating cortically descend to medullary cardiovascular centers. In addition to these pressor control mechanisms, it is quite possible that performing a Valsalva Maneuver during isometric contractions contributes to the rise observed in systemic pressure. In a Valsalva maneuver, the breathing pattern is manipulated such that air is forcefully expired against a closed glottis, resulting in increased thoracic pressure. Recent studies have demonstrated that the Valsalva maneuver alone can increase systemic blood pressure significantly. [9,10] No previous investigators, however, have reported a study to examine the effect of training in favorable breathing patterns on blood pressure during isometric contractions. We hypothesized that if patients could learn to avoid straining maneuvers, the potentially dangerous rise in systemic pressure that accompanies isometric contractions might be attenuated. The purpose of this study, therefore, was to investigate the effect of using learned breathing techniques on pressor responses during isometric contractions.

Method

Subjects

Twenty-seven college-aged, nonathletic, female subjects (X age = 21.5 [+ or -] 1.5 years) were recruited and asked to complete a medical history questionnaire. Any candidate presenting significant cardiovascular, pulmonary, or lower limb orthopedic problems was disqualified from participation. All recruited subjects were normotensive and of good general health and had completed a physical examination within the last 12 months. They each gave informed consent for participation according to the guidelines specified by the Ithaca College Human Subjects Research Committee.

Equipment and Procedure

Subjects attended an introductory meeting to become familiar with the laboratory environment and equipment and to arrange a participation schedule. At their subsequent visit (ei, testing session prior to breathing technique training), each subject was comfortably seated at a Cybex [R] II isokinetic dynamometer (*1) and stabilized at the ankle, thigh, and hips with Velcro [R] straps. (*2) A surface electrode was placed in the fifth or sixth intercostal space along the midaxillary line on each side of the subject. An impedance pneumograph and a four-channel physiograph were used to measure chest excursion during exercise. Two resting systemic blood pressure readings were then recorded using a mercury sphygmomanometer and a Bosch electronic stethoscope (*3) auscultating at the left brachial artery. This technique provided a clearly audible determination of Korotkoff sounds at rest and during the isometric contractions. Following assessment of resting blood pressure, subjects performed 10 submaximal knee extensions at a speed setting of 80 [degrees]/sec as a warm-up to testing. Each subject then performed 10 maximal isometric contractions with her right leg immobilized at 65 degrees of knee flexion. Each contraction lasted 10 seconds, with a 5-second relaxation period between contractions. Blood pressures were recorded during the 5th and 10th contractions, at which time the monitored arm was supported by the technician. Peak torque, or maximal voluntary contraction (MVC), was determined as the greatest value attained during the 10 contractions.

Following the pretraining testing session, subjects were randomly and equally assigned to one of three groups. The first group (VAL Group) was instructed to take a full inspiration prior to contractions and to expire against a closed glottis, thereby performing a forced Valsalva maneuver during contractions. The second treatment group (NO-VAL Group) was taught to take a full inspiration prior to each contraction and to exhale continuously during each contraction, thereby avoiding performance of the Valsalva maneuver. The control group (CONT Group) was given no directions for breathing. During three subsequent breathing technique training sessions, the subjects performed the exercise protocol previously described while performing their assigned breathing technique. To help control diurnal variation in blood pressure, individuals scheduled each training session and the posttraining testing session at the same time of day as their pertraining appointment. Posttraining testing was conducted in a fashion identical to pretaining data collection at least 24 hours after the final exercise session. For each subject, less than 10 days elapsed between the completion of pretraining and posttraining testing.

Data Analysis

Results were subjected to a 2-X-2-X-3 (time X trial X group) multivariate analysis of covariance (ANCOVA), with the variable time representing pretraining and posttraining measurements, the variable trial representing the 5th and the 10th contractions, and the variable group representing the control and two training methods. Dependent variables were systolic blood pressure (SBP) and diastolic blood pressure (DBP). The covariates in this design were the SBP and the DBP, calculated as the average of 8 resting values after dropping the highest and the lowest values of 10 measured values. These resting measurements were made twice upon arrival for each visit (ie, the pretraining, three training, and posttraining sessions). In discussing the multivariate ANCOVA results, SBP and DBP are referred to collectively as systemic pressure. Significant multivariate ANCOVA results were further examined using a univariate ANCOVA. Finally, we decided that if a significant decrease in systemic pressure for the NO-VAL Group was seen across time, this finding would be followed by planned comparisons of the posttraining univariate ANCOVA means for the CONT and NO-VAL Groups using the Student's t test. Assuming there were no pretraining differences between the groups, the planned comparisons would indicate whether those subjects who were given breathing instruction to avoid the Valsalva maneuver had significantly lower pressor responses to exercise than those subjects who had not training. Penumographic data were interpreted qualitatively to determine whether subjects were complying with the learned breathing techniques during training and testing sessions.

Results

No significant three-way interaction was found among the variables times, trial, and group. A two-way group-x-time interaction, however, indicated a significantly different blood pressure response from the pretraining to the posttraining testing sessions between the groups (p [is less than] .05). A univariate ANCOVA demonstrated that the time effect across the groups was the same for both SBP and DBP. Tables 1 and 2 show that the post-training SBP and DBP values increased for the VAL Group and decreased for the NO-VAL Group as compared with the pretraining values. Moreover, planned comparisons revealed that the posttraining SBP and DBP values for the NO-VAL Group were significanlty less than for the CONT Group, further emphasizing the pressor response attenuating ability of breathing instruction (Figure).

A univariate ANCOVA of the main effect for the variable trial confirmed that both SBP and DBP rose significantly from the 5th to the 10th contraction for all groups; howevr, analysis of the simple main effects revealed that posttraining SBP in the NO-VAL Group was not significantly affected by trial (Tab. 3).

Pneumographic data were inspected visually and interpreted qualitatively. All subjects demonstrated irregular breathing patterns and occasional (or partial) Valsalva maneuvers during pre-training testing. During posttraining testing, the VAL Group classically performed one or two Valsalva maneuvers in the time period required to perform a contraction and demonstrated breathing patterns with sustained periods of inspiration. The NO-VAL Group graphically demonstrated a sinusoidal curve representing rhythmic inspiration and expiration during posttraining testing, whereas the CONT Group continued to demonstrate breathing patterns similar to pretraining patterns. Effort was similar between groups when expressed as a percentage of MVC, although the NO-VAL Group developed greater absolute peak torques both before and after training compared with the VAL and CONT Groups (Tab. 4).

Discussion

The intent of this study was to determine whether learned rhythmic breathing techniques could eliminate performance of the Valsalva maneuver and thereby attenuate increases in blood pressure typically observed during isometric efforts. Performance of the Valsalva maneuver can significantly increase SBP because of an increase in heart rate and peripheral resistance, although stroke volume is decreased because of impaired venous return. (10) Greater peripheral resistance during straining can likely be attributed to increased intrathoracic pressure associated with the Valsalva maneuver. (9) In the present study, the ability of the VAL Group to increase SBP to significantly higher levels from pretraining to posttraining testing sessions exemplifies the potency of a forced Valsalva maneuver on pressor responses and supports previous reports.

A significant increase in SBP from the 5th to the 10th contraction was recorded during the isometric exercise regimen for all groups. This increase may be attributed to the fact that as more repetitions are performed, muscle fibers fatigue, and increased involvement of accessory muscles, including those associated with the Valsalva maneuver, may occur. Increased peripheral resistance attributable to greater intrathoracic pressure associated with the straining efforts may account for the systemic pressure elevations observed in this study, particularly in the VAL and CONT Groups during the posttraining test. The ability of the NO-VAL Group to avoid a significant increase in SBP from the 5th to the 10th contraction (lack of a simple main effect) may be attributed in part to avoidance of the Valsalva maneuver. (9) Learning rhythmic breathing techniques leads to avoidance of the Valsalva maneuver and consequently attenuates an increase in intrathoracic pressure and the contraction of accessory muscles, thereby checking the blood pressure rise. Any further increase in pressor response other than those immediate changes that occur with forced isometric contractions may be averted.

Pneumographic data indicated that all subjects performed some type of Valsalva or partial Valsalva maneuver during pretraining contractions. Moreover, prior to breathing technique training, the three groups had very similar pressor responses to isometric contractions. As discussed above, systemic blood pressure rose significantly from the pretraining test to the posttraining test for the VAL Group. Conversely, the results indicated that SBP and DBP decreased in the NO-VAL Group. Williams and Lind recently reported that straining accounts for about 20 mm Hg of the rise in mean arterial pressure (MAP) associated with isometric exercise. (11) In the present study, a consciously performed Valsalva maneuver during exercise resulted in a 13-mm Hg rise in MAP (DBP + 0.33[pulse pressure]), and learned avoidance of the maneuver prevented a 10-mm Hg increase in MAP for the NO-VAL Group. In support of the work of Williams and Lind, [11] therefore, we conclude that straining during isometric efforts can account for a 20- to 25-mm Hg rise in MAP. Accordingly, we suggest that learning proper breathing techniques may reduce elevations in systemic blood pressure associated with isometric contractions by eliminating performance of a Valsalva maneuver. This reduction is upported by significantly lower posttrating SBP and DBP measured in the NO-VAL Group compared with the CONT Group. The mechanism underlying attenuation of the pressor response is likely related to attenuation of the intrathoracic pressure rise caused by stabilization of the abdominal and thoracic musculature during a straining maneuver. Additionally, reflex sympathetic activity that normally follows the Valsalva maneuver [12] would also be avoided.

The decreased pressures observed in the NO-VAL Group possibly reflect decreased effort during the exercise. It is known that performance of the Valsalva maneuver allows increased stabilizaiton of postural and proximal muscle groups, thereby enhancing the ability of the prime mover to generate torque. It is also known that a greater active muscle mass elicits greater pressor responses. [7] The work of Mitchell et al, however, was performed by varying muscle mass involvement at 40% of MVC. [7] Freyschuss, in the late 1960s, demonstrated that no relationship exists between cardiovascular response during isometric contractions and the degree of effort above 70% of MVC. [13] Furthermore, Asmussen has confirmed that leg extension greater than 30% of MVC will elicit maximal occlusion of blood flow and nearly maximize circulatory respnse. [2] All contractions (ie, leg extentions) in this study were performed at greater thatn 75% of MVC, and peak torque values were not significantly different before or after training within each group. Moreover, although the percentage of MVC was similar between groups, the NO-VAL Group developed greater absolute peak torques than the CONT Group during posttraining testing. It is unlikely, therefore, that the influence of effort on circulatory response could be held accountable for blood pressure differences observed between the groups.

Pneumographic data revealed that some type of Valsalva maneuver was used by the CONT Group during both pretraining and posttraining testing. Individuals seemingly perform a Valsalva maneuver unconsciously when confronted with near-maximal efforts. The CONT Group demonstrated no significant change in SBP from pretraining to posttraining testing sessions. This finding demonstrates failure by the CONT Group to spontaneously learn an advantageous breathing pattern over three exercise sessions and imphasizes the need to provide clear breathing instructions if attenuation of the pressor response to isometric efforts is desired.

Conclusion

The results of this study support the hypothesis that the performance of a forced Valsalva maneuver increases the blook pressure responses associated with isometric contractions. Furthermore, instruction in breathing to avoid the Valsalva maneuver attenuates the blood pressure response associated with isometric exercise. Unfortunately, if no instructions are given, it does not appear that any spontaneous adaptation occur with exercise training that reduce the pressor response to isometric exercise. We, therefore, conclude that avoiding the performance of the Valsalva maneuver lowers blook pressure during isometric constractions and may have clinical implications for the safer administration of resistive exercise.

Acknowledgment

We wish to thank WH Ware, Department of Health, Physical Education, and Recreation, Ithaca College, for his insight and assistance.

(*1) Cybex, Div of Lumex, Inc. 2100 Smithtown Ave, Ronkonkoma, NY 11779.

(*2) Velcro USA, Inc, PO Box 5218, 406 Brown Ave, Manchester, NH 03108.

(*3) Model EST-40, Bosch Hearing Instruments, Div of Robert Bosch Technical Products Corp, PO Box 278, ST Jane, NY 11780.

REferences

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[11] Williams CA, Lind AR: The influence of straining maneuvers on the pressor response during isometric exercise. Eur J Appl Physiol 56:230-237, 1987

[12] Deering AH, Harron DWG: Valsalva's manoeuvre. International Pharmacy Journal 1:48-52, 1987

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P O'Connor, MS, PT, is Physical Therapist, Sportsfocus, Buffalo, NY and is completing a master's degree in sports medicine at Ithaca College, Ithaca, Ny 14850.

G Sforzo, PhD, is Associate Professor, Department of Exercise and Sport Sciences, Ithaca College, Ithaca, NY 14850 (USA). Address corespondence to Dr Sforzo.

P Frye, PED, is Associate Professor, Department of Exercise and Sport Sciences, Ithaca College.