Hemodynamic patterns and duration of post-dynamic exercise hypotension in hypertensive humans

Medicine & Science in Sports & Exercise: Volume 28(1) January 1996 pp 24-32 Hemodynamic patterns and duration of postdynamic exercise hypotension in hypertensive humans RUECKERT, PATRICIA A.; SLANE, PETER R.; LILLIS, DIANE L.; HANSON, PETER Department of Medicine, Cardiology Section, University of Wisconsin Medical School, Madison, WI 53792-3248 Submitted for publication February 1995 Accepted for publication August 1995 We thank the patients who participated in this study and Shari Clark for her technical assistance with the hemodynamic measurements Address for correspondence: Patricia A Rueckert, Ph.D., Cardiology Section H6/349, University of Wisconsin Medical School, 600 Highland Avenue, Madison, WI 53792-3248 ABSTRACT TOP We investigated: 1) the mechanism of the hypotensive effect of a single bout of dynamic exercise in hypertensive subjects by measuring hemodynamic parameters before and for h after treadmill exercise, and 2) the duration of the effect using ambulatory blood pressure (BP) monitoring once the subjects left the test site Ten minutes after exercise there was a significant decrease from baseline systolic pressure (SP; -14 ± mm Hg), mean arterial pressure (MAP; -7 ± mm Hg), total peripheral resistance(TPR; -3.7 ± 1.2 units), calf vascular resistance (CVR; -25.4 ± 4.1 units), and an increase in HR (19 ± bpm) The changes in SP, DP, MAP, and HR were maintained during the h of post-exercise monitoring; CVR remained decreased for h; TPR returned to baseline within 20 and then tended to be slightly elevated CO was significantly decreased at 50, 60, and 120 after exercise We conclude that the early decline in BP after dynamic exercise in hypertensive subjects follows a biphasic pattern: 1) an initial decrease in total and regional vascular resistance with maintained CO, 2) followed by increasing resistance and decrease CO Pre-exercise hypertensive BP values returned during subsequent ambulatory monitoring Resting blood pressure (BP) in hypertensive individuals is often lower or normalized after exercise training (2,22) as well as after a single bout of dynamic exercise(9,13,18,21,23,33,40) There is less consensus concerning the hypotensive effect of an acute bout of exercise in normotensive individuals, although there are also reports of lowered BP after such exercise in this group(10,21,40) The mechanism of thispost-exercise hypotension, however, is poorly understood Reported decreases in regional vascular resistance after a single bout of dynamic exercise (9,10) may be due to lowered efferent muscle sympathetic nerve activity (13), reduced alpha-adrenergic responsiveness (17), vasodilatory metabolites (10,21), or thermoregulatory-induced increases in skin blood flow (15) Although most investigators observe a decrease in total peripheral resistance (TPR)(9,21), this is not a universal finding Changes in post-exercise heart rate (HR) and cardiac output (CO) have also been inconsistent and may be influenced by exercise intensity or initial hemodynamic state of the subjects Hagberg et al (18) found that older subjects had decreased CO because of a reduced stroke volume(SV) and unchanged HR after exercise, whereas other studies found increased CO(9) and HR (13) Reductions in CO were suggested as the primary hemodynamic mechanism for the post-exercise hypotension in hypertensive rats (32) Few investigators have addressed the question of the duration of the acute post-exercise decline in BP Using ambulatory BP monitoring, Pescatello et al.(33) concluded that postexercise BP were lower than pre-exercise levels for 8-12 h after exercise Somers et al.(40), however, could demonstrate no sustained drop in either systolic (SP) or diastolic pressure (DP) once their subjects left the lab and took their own BP at home Thus, many unanswered questions remain regarding not only the mechanism of the acute hypotensive effect of dynamic exercise but the time course and duration of the effect Our study is unique in that it measured central and peripheral hemodynamics during the first h after exercise and then continued to assess the duration of BP changes using ambulatory blood pressure monitoring We hypothesized that regional vasodilation in the legs contributing to a decrease in TPR after treadmill exercise would play an important role in the post-exercise decline in BP Frequent measurements were designed to allow the determination of the time course of both central and regional hemodynamic changes early after exercise Since only two studies with conflicting results have examined the duration of the hypotensive response to dynamic exercise, it was hoped that our study would provide additional needed information on this aspect of post-exercise hypotension METHODS TOP Subjects TOP Eighteen nonsmokers (50 ± yr of age; height 177 ± cm; weight 87 ± kg; females, 13 males) with Stage to Stage essential hypertension participated in the study They were former participants in research and clinical protocols in our laboratory and were familiar with exercise testing and the measurement procedures we used Eight of the subjects had never taken medication for hypertension and the others were taking ACE inhibitors (N = 4), calcium channel antagonists(N = 2), betablockers (N =3), or diuretics (N = 1) None were receiving antihypertensive therapy during the study; those treated pharmacologically for hypertension stopped taking their medications at least wk before the study Subjects gave written consent for participation in the study, which was approved by the University of Wisconsin-Madison Center for Health Sciences Human Subjects Committee and was in accordance with the policy statements of the American College of Sports Medicine Protocol TOP On the exercise day, subjects reported to the lab at 0800 They were asked to avoid caffeine that morning but were told to eat breakfast if it was their normal routine ECG and transthoracic CO impedance electrodes were applied, and a flexible intravenous catheter was inserted into an antecubital vein for multiple blood sampling Subjects then moved to a semi-recumbent position on a padded table and rested for 15 while the measuring instruments were calibrated Pre-exercise hemodynamic measurements were made and a blood sample was obtained The subjects then moved from the table, went to the bathroom if necessary, and were weighed to the nearest 0.1 kg After a brief warm-up period on the treadmill, the subjects walked for 45 at a speed and grade that was adjusted to maintain their HR at 70% of HR reserve (Resting HR + 0.70[Predicted max HR - Resting HR]) BP were measured every by sphygmomanometry and HR were continuously monitored by ECG and recorded every Room temperature was maintained at 23-24°C throughout the morning Subjects were weighed after exercise, rehydrated by mouth with water equivalent to the weight lost during exercise, and resumed the semi-recumbent resting position for the next 60 Post-exercise hemodynamic measurements were made every 10 during this hour Blood samples were drawn at 10, 30, 60, and 120 During the second hour, subjects moved from the padded table, the ambulatory BP monitor was positioned, and comparisons were made between auscultatory BP in the seated and standing positions and monitor readings A final set of post-exercise hemodynamic measurements was made h after exercise when the subjects had again been in the semirecumbent position for 10 Resting Control Study TOP A subset of subjects was asked to return to the test site at a later date to study the effect of 45 of rest followed by h of semi-recumbency on the hemodynamic parameters The subjects were told that they were returning for a reproducibility study of the treadmill exercise protocol Afterpre-exercise measurements were made, the subjects were then told to relax in a chair for 45 instead of exercise Hemodynamic measurements were performed every 10 for h after this rest period Hemodynamic Measurements TOP BP were measured with a mercury manometer by the same person and in the same arm; disappearance of the fourth Korotkoff sound was used as the DP HR was obtained from the ECG Calf blood flow (CBF) was measured by venous occlusion plethysmography (17) and calf vascular resistance (CVR) calculated from mean arterial pressure (MAP)/CBF Transthoracic impedance cardiography utilizing R-wave triggered computerized ensemble signal averaging analysis (SORBA Medical Systems, Inc., Brookfield, WI) was used to determine SV and CO CO obtained with this technology are equivalent to those determined by thermodilution(30,34) over a broad range of values and are particularly reliable when used for repeated resting measurements as was done in this study In our hands, the coefficient of variation for resting measurements is 5.5% TPR was calculated from MAP/CO and the Heather Index(HI) for cardiac contractility was calculated from the quotient of dZ/dtmax/QZ1 (30) DZ/dtmax, the magnitude of the peak value of the impedance derivative, correlates closely with aortic velocity (26) The quotient of dZ/dtmax and the pre-ejection time (Q) and rapid ejection time (Z1) provides a timed index of myocardial contractility (26) Plasma Volume Change Determination TOP The hematocrit (Hct), measured in duplicate using a microhematocrit method, was corrected for plasma trapped with red blood cells and for venous-to-total body Hct ratio (7) Hemoglobin (Hb) was measured in duplicate on a Copenhagen OSM3 Hemoximeter Hct and Hb values were used to calculate percentage change in plasma volume using the equations of Dill and Costill (12) Ambulatory BP Monitoring TOP Thirteen of the hypertensive subjects underwent ambulatory BP monitoring with a Suntech Accutracker II monitor on two days: 1) a nonexercise control day and 2) after the hemodynamic measurements on the exercise day Subjects were asked to plan similar levels of activity for the two days of monitoring but otherwise went about their normal activities The recording was considered acceptable if at least 85% of the readings met the editing criteria BP were deleted if DP were ≥ 130 mm Hg, if systolic blood pressures (SP) were240 mm Hg, or if the pulse pressure was