Mean Exercise Heart Rate Research Articles

Are subjective reports of exercise intensity accurate in recreational athletes?

Quantifying exercise intensity accurately is crucial for understanding links between cumulative exercise and cardiovascular outcomes. Exercise burden, the integral of intensity and duration is often estimated from subjective self-reports which have uncertain accuracy. We studied 40 endurance athletes (EA) 41 to 69 yrs. with >10 yrs. training history during a scripted outdoor 42 km cycling training session. Heart rate (HR) and power output (Watts) were continuously measured. Reports of perceived exertion (RPE) using a word (RPEWord) and numerical Borg scale (RPEBorg) were obtained during and 30 min. post ride and were related to cardiac (HR) and metabolic (MET·min) exercise endpoints. RPEs were highly variable, underestimating objective metrics of exercise intensity. Poor agreement was observed between either scale reported 30 minutes after exercise relative to heart rate: exercise RPEBorg vs. mean exercise HR and %HRpeak (both rs=.29, p=0.07), with no agreement between either scale vs. other objective endpoints. Agreement between RPEBorg and RPEWord was good during exercise (rs=0.86, 95% CI 0.75 to 0.92, P=0.001), but diminished post ride (rs=0.54, 95% CI 0.28 to 0.73, P=0.001). Different cardiac and metabolic profiles during exercise and a contrast between metabolic and cardiac burden was greater in less fit individuals as they accrued greater cardiac (14039±2649 vs. 11784±1132 HR·min, P<0.01) but lower metabolic (808±59 vs. 858±61 MET·min, P<0.05) burden vs. fitter EA. Caution is advised in interpreting MET·min and HR burden estimated from self-reports. Objective measurements of exercise intensity are required for detailed assessment of the risks and benefits of long-term exercise.

The heart rate response to the 6-min walk test in atrial fibrillation patients with or without beta-blockers: Referring to patients with sinus rhythm.

The aim was to evaluate the effect of beta-blockers (BB) on the response of heart rate (HR) to 6-min walk test (6MWT) in atrial fibrillation (AF) and whether the AF patients treated with BB have a similar HR response to 6MWT as the AF and sinus rhythm (SR) patients without BB treatment at the same resting HR level. The before-after study involving 74 AF patients was to evaluate the effect of BB treatment (pre-BB and with BB). The comparison study included 74 BB-treated AF patients (with BB), 74 matched AF patients without BB (no BB), and 74 SR patients. The percentage increase amplitude of HR (HR-PIA) in 6MWT was calculated: [(the exercise HR - the resting HR)/(the resting HR)] × 100%. The before-after study showed that BB treatment decreased the resting and mean exercise HR (98.6 ± 15.2 vs. 85.5 ± 11.2 bpm and 121.3 ± 17.3 vs. 109.0 ± 16.7 bpm) during 6MWT. The comparison study demonstrated that against the SR, the AF with BB and no BB groups have higher mean exercise HR-PIA (28.2 ± 17.1% and 22.0 ± 9.6%, vs. 6.9 ± 3.7%) when their resting HR is similar. Moreover, the mean exercise HR-PIA was also significantly higher in the with BB group than in the no BB group. In AF patients with relatively higher resting HR, BB treatment could decrease the resting and exercise HR during 6MWT. However, BB treatment could not effectively attenuate the exercise HR rise as compared with AF without BB treatment, even with similar resting HR levels.

SAFETY AND EFFICACY OF SURGICAL PREHABILITATION IN CARDIOVASCULAR SURGERY PATIENTS

https://youtu.be/rQFd3dU-8AM BACKGROUND There are many complications that patients experience after cardiothoracic surgery, including prolonged intubation, increased length of ICU stay, infection, cardiovascular and muscular deconditioning and decreased quality of life. To reduce post-surgical complication risk, pre-surgical rehabilitation (Prehab) has developed as a potential countermeasure. Prehab may include exercise training, nutrition counseling, social support, patient and family education, smoking cessation and weight management. METHODS Thirty-nine, high risk surgical patients scheduled for major cardiovascular surgery were referred to the Prehab program by their cardiovascular surgeon to prepare them for upcoming intervention. Each patient underwent pre- and post-assessments, to include a six-minute walk test (6MWT), hand grip dynamometry (GRIP), and 30-second chair stands (30SCS). Patients attended supervised exercise sessions twice weekly for at least 2 weeks leading up to their surgical procedure. The 60-minute session included symptom-limited aerobic and resistance training, along with education on nutrition and post-surgical expectations. Dependent samples t-tests were used to determine statistical significance for all pre-post comparison measures. RESULTS Average program duration was 6.3 ± 3.3 wk, average number of sessions attended was 9.9 ± 5.7 sessions and the average number of sessions per week was 1.7 ± 0.3 sessions per week. Patients exercised for 27.1 ± 5.0 min with a mean exercise heart rate at 20.7 ± 12.4 bpm above rest. There were significant increases in 30SCS (pre = 9.5 ± 4.2 reps vs. post = 11.3 ± 4.5 reps), 6MWT (pre = 343.2 ± 117.9 m vs. post = 386.1 ± 96.9 m) and MET-min -1 (pre = 64.8 ± 27.5 MET-min -1 vs. post = 87.6 ± 7.3 MET-min -1). There were no changes in weight (pre = 87.5 ± 19.7 kg vs. post = 87.7 ± 19.3 kg), BMI (pre = 29.0 ± 6.2 kg·m 2 vs. post = 29.0 ± 6.0 kg·m 2), or GRIP (15.5 ± 6.7 kg vs. post = 17.8 ± 9.6 kg). Regarding safety, 385 exercise sessions were completed by all patients and 7 sessions were deferred by the staff for clinical reasons. In addition, of the 422.5 patient-hours of exercise, no untoward events occurred. CONCLUSION Patients awaiting cardiovascular surgery can exercise safely at a low to moderate intensity and see improvements in functional capacity and muscular strength.

Monitoring Elite Youth Football Players' Physiological State Using a Small-Sided Game: Associations With a Submaximal Running Test.

To examine the utility of a standardized small-sided game (SSG) for monitoring within-player changes in mean exercise heart rate (HRex) when compared with a submaximal interval shuttle-run test (ISRT). Thirty-six elite youth football players (17 [1]y) took part in 6 test sessions across an in-season period (every 4wk). Sessions consisted of the ISRT (20-m shuttles, 30″:15″ work:rest ratio, 70% maximal ISRT) followed by an SSG (7v7, 80 × 56m, 6min). HRex was collected during both protocols, with SSG external load measured as high-speed running distance (>19.8km·h-1) and acceleration distance (>2m·s-2). Data were analyzed using linear mixed-effect models. Controlling for SSG external load improved the model fit describing the SSG-ISRT HRex relationship (χ2 = 12.6, P = .002). When SSG high-speed running distance and SSG acceleration distance were held constant, a 1% point change in SSG HRex was associated with a 0.5% point change in ISRT HRex (90% CI: 0.4 to 0.6). Inversely, when SSG HRex was held constant, the effects of a 100-m change in SSG high-speed running distance and a 21-m change in SSG acceleration distance on ISRT HRex were -1.0% (-1.5 to -0.4) and -0.6% points (-1.1 to 0.0), respectively. An SSG can be used to track within-player changes in HRex for monitoring physiological state. Given the uncertainty in estimates, we advise to only give meaning to changes in SSG HRex >2% points. Additionally, we highlight the importance of considering external load when monitoring SSG HRex.

Effect of shoulder pain on energy expenditure among paraplegic individuals: Role of wearable device

Background: Human interactive wearable devices are cutting-edge technologies transforming the health-care system by allowing comfort, convenience, and continuous patient monitoring. Wheelchair use in spinal cord injury is the best form of mobility. Shoulder pain is often the consequence to increased kinetic demands placed on the upper limb. This paper is an endeavour to determine the effect of shoulder pain on energy expenditure amongst manual wheelchair users with an amalgamation of physiological health parameters and advancement in health monitoring technology. Methodology: Forty paraplegics using manual wheelchairs were divided into two groups depending on the presence of shoulder pain. Shoulder pain characteristics were noted using the Wheelchair Users Shoulder Pain Index. Mean heart rate during 6 min propulsion test was determined using the Xiaomi MI fitness band. Physiological Cost Index was established, and the energy expenditure was then compared. Results: Shoulder pain was reported maximum during pushing the wheelchair >10 min (80%) and on-ramps (65%). The energy expenditure showed a statistically significant increase in patients with shoulder pain. Conclusion: The use of Xiaomi MI fitness band is a straightforward and affordable way to obtain the mean exercise heart rate assisting in estimating the energy expenditure. Shoulder pain significantly increases the energy expenditure among manual wheelchair users, and hence should be addressed before wheelchair use for the prevention of injuries.

Heart Rate Equivalency of the Fitbit Charge HR During Continuous Aerobic Exercise

Purpose: Consumer-grade wrist-worn activity monitors frequently include photoplethysmography (PPG) sensors for estimating heart rate (HR). The Fitbit Charge HR is marketed specifically for tracking fitness; therefore, HR accuracy is critical, especially during exercise. This study examined HR equivalency of the Fitbit Charge HR during continuous aerobic exercise. Method: Participants (N = 19) concurrently wore a Polar H1 and Fitbit Charge HR during a measurement visit that included seated rest (5 minutes), warm-up (5 minutes), continuous treadmill exercise (30 minutes), and cool-down (5–10 minutes). Mean HR differences were examined by protocol phase, total activity (i.e., warm-up, exercise, and cool-down combined), and the first, middle, and last 5 minutes of continuous exercise. Mean absolute percent error (MAPE), Bland-Altman plots, and 95% equivalence testing explained overall and individual HR agreement between devices. Results: The Fitbit Charge HR significantly underestimated HR for all measurement phases (all p ≤ .01) except cool-down (p &gt; .33). HR agreement was notably weaker during warm-up (r = 0.66, d = 0.57) and differences were greatest for the first 5 minutes compared to the middle and end of exercise (6.94±2.16 beats per minute [bpm] vs. 1.76±0.59 bpm, and 1.74±0.58 bpm), F = 4.87, p = .04). Mean exercise HRs were equivalent between devices (±2.69 bpm, 95% CI: 1.41–3.97 bpm); MAPE was 1.96%. Conclusion: The Fitbit Charge HR is relatively accurate for measuring HR during continuous aerobic exercise. Whereas the accuracy of PPG-based HR appears limited at exercise onset, agreement improves throughout the exercise bout and HR differences are negligible.

Determining target heart rate for exercising in a cardiac rehabilitation program: a retrospective study.

One of the well-established methods used to determine endurance training intensity for patients in outpatient cardiac rehabilitation (CR) is to take a percentage (70%-85%) of the maximal or peak heart rate (HRmax) from a recent postevent symptom-limited graded exercise test (GXT). Because many patients are referred to CR without having had a maximal GXT, a current practice is to use 30% to 50% above resting heart rate (RHR) to estimate endurance training intensity. The purpose of this study was to determine if a target heart rate (THR) of 30% to 50% above RHR approximated a THR of 70% to 85% of the HRmax achieved on GXT (HRmax GXT) and provided equivalent exercise intensity based on ratings of perceived exertion (RPE) and metabolic equivalency thresholds (METs). A retrospective chart review of 53 patients enrolled in CR and had documentation of postevent GXT was conducted to determine the patient's mean exercise heart rate (HR) achieved at each session to percentage above RHR and percentage HRmax GXT. Analysis was conducted to determine and compare patients' HRs, RPE, and MET levels when patients were exercising within the THR ranges of 30% to 50% above RHR and 70% to 85% HRmax GXT. A THR range of 30% to 50% above RHR approximated 60% to 70% HRmax GXT. Mean exercise HRs progressed from 39% to 49% above RHR sessions 2 to 6 with mean (SD) RPE of 10.58 (0.55) to 11.44 (0.68) on the Borg scale and mean (SD) MET level of 2.91 (0.55) to 3.31 (0.6). Mean exercise HRs progressed to 54% to 65% above RHR sessions 7 to 18 and approximated 70% to 73% HRmax GXT. Mean (SD) RPE at this intensity ranged from 11.57 (0.58) to 12.21 (0.53) with a mean (SD) MET level of 3.47 (0.6) to 3.8 (0.77). In the observed population, a THR of 30% to 50% above RHR underestimated the THR range of 70% to 85% HRmax GXT but provided adequate exercise intensity for patients at the beginning of a CR program based on percentage HRmax GXT, RPE and MET levels.

Two days of staging at moderate altitude results in similar time‐trial performance impairments at 4300m compared to direct ascent and stay for two days at 4300m

Staging at moderate altitude or direct ascent and stay at high altitude (HA) are strategies used to reduce time‐trial (TT) performance impairments at HA. To determine whether 2 days (d) of staging at 2500m or 3000m prior to ascent is as effective as 2 d of continuous living at 4300m, we measured TT performance following 2 h of exposure to 4300m in young fit men. Two groups of unacclimatized men staged at either 2500m (n=12) or 3000m (n=7) for 2 d prior to ascent to 4300m were compared to a 3rd group that directly ascended and lived for 2 d at 4300m (n=7) prior to testing. Acute mountain sickness (AMS‐C) was assessed prior to performing an all out 5‐mile treadmill TT at sea level (SL) and HA. Heart rate (HR), arterial oxygen concentration (SaO2), and rating of perceived exertion (RPE) were recorded every 5 min during the TT and the mean value was calculated. From SL to ALT, the %increase in TT‐completion time was similar (P&gt;;0.05) in the 2500 m (44±27%), 3000 m (39±27%) and direct ascent group (58±28%). There was no difference (P&gt;;0.05) in the mean exercise HR, SaO2, or RPE between groups at SL or HA. AMS prevalence was lower (P&lt;0.05) in the staged groups (both 0%) than the direct ascent group (29%). These results suggest that 2 d of staging at moderate altitude reduces AMS but results in similar TT performance impairments as direct ascent and stay for 2 d at 4300 m. Funding: USAMRMC. Authors’ views; not official US Army or DoD policy.

Hydration, Thermoregulation, and Performance Effects of Two Sport Drinks during Soccer Training Sessions

In the present study, we aimed to compare the thermoregulatory response and soccer-specific training performance aspects of two commercially available sport drinks, both of similar carbohydrate concentration, but one containing 5.2% glycerol. Ten players participated in two similar outdoor training sessions and were randomly assigned to each of two drinks: a carbohydrate (C) beverage or a carbohydrate-glycerol (CG) beverage. Players consumed 500 mL of C or CG 30 minutes pre-exercise and at half-time. Pre- and postexercise body mass, core temperature (CT), and heart rate (HR) were recorded, and urine and blood samples were taken. No difference was observed between days for wet bulb globe temperature (session 1: 17.0 +/- 1.1 degrees C, session 2: 16.9 +/- 1.1 degrees C; P = 0.944). The degree of dehydration (% Delta BM) was greater after the C trial (P = 0.041). Similarly, percent change in plasma volume was greater in the C trial (P = 0.049). No overall main affect was observed between CT and mean exercise HRs during either training session (CT: P = 0.350; mean HR: P = 0.256), and there was no difference observed between groups in time to failure during the session-ending fatigue test (P = 0.547). Ingestion of a CG beverage provided players with better hydration than C alone. However, if training sessions are short (<75 minute), with adequate time for recovery, both drinks are sufficient for maintaining performance intensities during soccer-specific training.

The Effect of Experience and Gender on Cardiovascular and Metabolic Responses With Dynamic Tae Kwon Do Exercise

This study, conducted at the Exercise Physiology Laboratory of Auburn University AL, addressed and compared the acute cardiovascular and metabolic effects elicited by novice and experienced men and women participants during a single bout of dynamic Tae Kwon Do exercise and investigated whether or not dynamic Tae Kwon Do practice is an exercise modality that provides sufficient cardiorespiratory demand for enhancing aerobic fitness and promoting weight and fat loss. Twenty-eight men and women (aged 19–42) were assigned to 1 of the following 4 groups: Tae Kwon Do experienced and trained men (ME), Tae Kwon Do experienced and trained women (FE), novice Tae Kwon Do men (MN), and novice Tae Kwon Do women (FN). The results of this investigation indicate that this form of exercise can be performed for an extended period of 20 minutes. All 4 groups achieved the recommended stimulus for effective initiation of cardiovascular adaptations and conditioning. The mean exercise heart rate responses (88.3–92.2% of maximal heart rate [HR max]) were similar for all groups. The observed exercise intensity ranged from 67.9 to 72.1% Vo2max, and no significant difference based on the experience and gender and exercise oxygen uptake could be established. Data in this study indicate a high caloric expenditure for this mode of exercise. Total caloric cost of 20 minutes of dynamic Tae Kwon Do, 194.8 and 201.6 kcal for novice women and experienced women, respectively, was significantly lower in comparison with that of their men counterparts (316.5 and 286.5 kcal, respectively), but no significant relationship between experience and energy cost was found. The conclusion of this study indicates that dynamic Tae Kwon Do is an exercise modality that can be appropriately prescribed for cardiovascular conditioning, weight control, and fat loss.

The Effect of Experience and Gender on Cardiovascular and Metabolic Responses With Dynamic Tae Kwon Do Exercise

This study, conducted at the Exercise Physiology Laboratory of Auburn University, AL, addressed and compared the acute cardiovascular and metabolic effects elicited by novice and experienced men and women participants during a single bout of dynamic Tae Kwon Do exercise and investigated whether or not dynamic Tae Kwon Do practice is an exercise modality that provides sufficient cardiorespiratory demand for enhancing aerobic fitness and promoting weight and fat loss. Twenty-eight men and women (aged 19-42) were assigned to 1 of the following 4 groups: Tae Kwon Do experienced and trained men (ME), Tae Kwon Do experienced and trained women (FE), novice Tae Kwon Do men (MN), and novice Tae Kwon Do women (FN). The results of this investigation indicate that this form of exercise can be performed for an extended period of 20 minutes. All 4 groups achieved the recommended stimulus for effective initiation of cardiovascular adaptations and conditioning. The mean exercise heart rate responses (88.3-92.2% of maximal heart rate [HR max]) were similar for all groups. The observed exercise intensity ranged from 67.9 to 72.1% VO2max, and no significant difference based on the experience and gender and exercise oxygen uptake could be established. Data in this study indicate a high caloric expenditure for this mode of exercise. Total caloric cost of 20 minutes of dynamic Tae Kwon Do, 194.8 and 201.6 kcal for novice women and experienced women, respectively, was significantly lower in comparison with that of their men counterparts (316.5 and 286.5 kcal, respectively), but no significant relationship between experience and energy cost was found. The conclusion of this study indicates that dynamic Tae Kwon Do is an exercise modality that can be appropriately prescribed for cardiovascular conditioning, weight control, and fat loss.

Aerobic performance of Special Operations Forces personnel after a prolonged submarine deployment

The US Navy's Sea, Air and Land Special Operations Forces personnel (SEALs) perform a physically demanding job that requires them to maintain fitness levels equivalent to elite athletes. As some missions require SEALs to be deployed aboard submarines for extended periods of time, the prolonged confinement could lead to deconditioning and impaired mission-related performance. The objective of this field study was to quantify changes in aerobic performance of SEAL personnel following a 33-day submarine deployment. Two age-matched groups of SEALs, a non-deployed SEAL team (NDST, n= 9) and a deployed SEAL team (DST, n= 10), performed two 12-min runs for distance (Cooper tests) 5 days apart pre-deployment and one Cooper test post-deployment. Subjects wore a Polar Vantage NVTM heart rate (HR) monitor during the tests to record exercise and recovery HR. Variables calculated from the HR profiles included mean exercise heart rate (HRmean), maximum exercise heart rate (HRmax), the initial slope of the HR recovery curve (HRreslope) and HR recovery time (HRrectime). The second pre-deployment test (which was used in the comparison with the post-deployment test) showed a 2% mean increase in the distance achieved compared with the first (n= 18, p< 0.05) with no difference in HRmean, HRmax, HRreslope and HRrectime. The test-retest correlation coefficient and 95% limits of agreement for the Cooper tests were 0.79 (p< 0.001) and −68.6±267.5 m, respectively. For the NDST there were no changes in any of the HR measures or the distance run between the pre- and post-deployment tests. When individual running performances were expressed as a percentage change in the distance run between the pre- and post-deployment tests, the DST performed significantly worse than the NDST (p< 0.01). The DST showed a 7% mean decrement in the distance run following deployment (p< 0.01). The decrement in performance of the DST was not associated with any changes in HRmean or HRmax; however, there was a 17% decrease in the HRrecslope (p< 0.05) and a 47% increase in HRrectime following the deployment (p< 0.05). In conclusion, prolonged confinement aboard a submarine compromises the aerobic performance of SEAL personnel. The resulting deconditioning could influence mission success.

Reduced levels of skeletal muscle Na+K+ -ATPase in McArdle disease.

We evaluated the hypothesis that impaired sarcolemmal function associated with exaggerated potassium release, impaired potassium uptake, or both may contribute to exertional fatigue and abnormal circulatory responses to exercise in McArdle disease (MD). The cellular mechanism of exertional fatigue and muscle injury in MD is unknown but likely involves impaired function of the ATPases that couple ATP hydrolysis to cellular work, including the muscle sodium potassium pump (Na+K+-ATPase). However, the concentration of muscle Na+K+ pumps in MD is not known, and no studies have related exercise increases in blood potassium concentrations to muscle Na+K+ pump levels. We measured muscle Na+K+ pumps (3H-ouabain binding) and plasma K+ in response to 20 minutes of cycle exercise in six patients with MD and in six sex-, age-, and weight-matched sedentary individuals. MD patients had lower levels of 3H-ouabain binding (231 +/- 18 pmol/g w.w., mean +/- SD, range, 210 to 251) than control subjects (317 +/- 37, range, 266 to 371, p < 0.0004), higher peak increases in plasma potassium in response to 45 +/- 7 W cycle exercise (MD, 1.00 +/- 0.15 mmol/L; control subjects, 0.48 +/- 0.09; p < 0.0001), and mean exercise heart rate responses to exercise that were 45 +/- 12 bpm greater than control subjects. Our results indicate that Na+K+ pump levels are low in MD patients compared with healthy subjects and identify a limitation of potassium reuptake that could result in sarcolemmal failure during peak rates of membrane activation and may promote exaggerated potassium-activated circulatory responses to submaximal exercise. The mechanism of the low Na+K+ pump concentrations in MD is unknown but may relate to deconditioning or to disruption of a close functional relationship between membrane ion transport and glycolysis.

Transdermal Timolol: β Blockade and Plasma Concentrations After Application for 48 Hours and 7 Days

An effective and well-tolerated transdermal beta-adrenergic blocker that could be applied once weekly would facilitate compliance. The pharmacokinetics and pharmacodynamics of a once-weekly formulation of transdermal timolol, a beta-blocker, were evaluated in healthy males. One (n = 6), two (n = 5), and three (n = 5) patches (97.5 mg base/12.58 cm2 patch) were applied at weekly intervals to the subjects' inner arm for 48 hours (part A) and two patches were applied for 7 days (part B). In part A, mean exercise (bicycle ergometry) heart rate (beats/min, bpm) was suppressed from baseline at 48 hours after the patch (p less than 0.05) in each case (1 patch 167 vs 131 bpm; 2 patches 165 vs 120 bpm; 3 patches 159 vs 120 bpm). Mean plasma timolol concentrations at 48 hours after the patch for one, two, and three patches were 5, 11, and 14 ng/ml, respectively. For part B, mean exercise heart rate at baseline, 24, and 168 hours was 161, 113, and 130 bpm (p less than 0.05), and mean plasma timolol concentrations at these times were 0, 23, and 4 ng/ml. The relationship between suppression of exercise heart rate and plasma timolol concentrations within subjects was well described by an inhibitory EMAX model, where EMAX ranged from a suppression of 42-65 bpm associated with a 50% inhibitory (IC50) concentration that ranged from 2-4 ng/ml. Transdermal timolol was associated with significant beta blockade for up to 7 days, and caused only minimal skin irritation.

Influence of menstrual cycle on thermoregulatory, metabolic, and heart rate responses to exercise at night.

Ten women [mean maximal O2 uptake (VO2max), 2.81 l X min-1] exercised for 15 min on a cycle ergometer in the middle of the luteal phase (L) and in the early follicular phase (F) of the menstrual cycle at the same constant work rates (mean 122 W) and an ambient temperature of 18 degrees C. Serum progesterone averaged 44.7 nmol X l-1 in L and 0.7 nmol X l-1 in F. After a 4-h resting period, exercise was performed between 3 and 4 A.M., when the L-F core temperature difference is maximal. Preexercise esophageal (Tes), tympanic (Tty), and rectal (Tre) temperatures averaged 0.6 degrees C higher in L. During exercise Tes, Tty, and Tre averaged 0.5 degrees C higher. The thresholds for chest sweating and cutaneous vasodilation (heat clearance technique) at the thumb and forearm were elevated in L by an average of 0.47 degrees C, related to mean body temperature (Tb(es) = 0.87Tes + 0.13Tskin), Tes, Tty, or Tre. The above-threshold chest sweat rate and cutaneous heat clearances were also increased in L. The mean exercise heart rate was 170.0 beats X min-1 in L and 163.8 beats X min-1 in F. The mean exercise VO2 in L (2.21 l X min-1) was 5.2% higher than in F (2.10 l X min-1), the metabolic rate was increased in L by 5.6%, but the net efficiency was 5.3% lower. No significant L-F differences in the respiratory exchange ratio and postexercise plasma lactate were demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of high-dose and medium-dose propranolol in the relief of exercise-induced myocardial ischemia

The effects of medium-dose (160 mg/day) and high-dose (480 mg/day) oral propranolol were compared in 22 patients who had typical angina pectoris and objective evidence of myocardial ischemia during exercise. Left ventricular (LV) ejection fraction (EF) and wall motion score (WMS) (an index of regional LV dysfunction) were assessed by radionuclide angiography both at rest and during exercise to the pretreatment maximum work load. Functional class improved in 11 of the 22 patients during medium-dose propranolol therapy. Medium-dose propranolol reduced mean resting heart rate from 71 to 55 beats/min, exercise heart rate from 122 to 93 beats/min, and exercise systolic blood pressure from 183 to 162 mm Hg (p < 0.001 for each). The incidences of exercise-induced chest pain and S-T segment depression were reduced from 19 to 9 patients (p < 0.001), and from 20 to 10 patients (p = 0.002), respectively. Medium-dose propranolol had no effect on mean EF or WMS at rest, but improved function in ischemic regions during exercise; WMS decreased (p = 0.001), and mean exercise EF increased from 0.51 to 0.56 (p = 0.025). Compared with the medium dose, high-dose propranolol improved functional class in 3 additional patients, and further reduced mean resting heart rate (from 55 to 52 beats/min, p = 0.001) and mean exercise heart rate (from 93 to 86 beats/min, p = 0.001). Exercise-induced chest pain and S-T segment depression were abolished in a further 7 and 6 patients, respectively. Exercise EF and WMS improved further in several patients, but the changes were not statistically significant for the group (p = 0.095 and 0.082, respectively). Thus, in patients with coronary artery disease and exercise-induced ischemia, propranolol reduced heart rate and blood pressure and the incidence of exercise-induced chest pain, electrocardiographic changes, and ischemic LV dysfunction. Although most of these effects were seen with medium-dose propranolol, higher doses provided additional relief of chest pain and S-T segment depression, and further improved global and regional LV function in several patients.

INTRINSIC HEART RATE ON EXERCISE AND THE MEASUREMENT OF β‐ADRENOCEPTOR BLOCKADE

Methods of expressing the effects of beta-adrenoceptor blocking drugs on exercise heart rate have been evaluated using a standardised exercise test. In six normal subjects given atropine (0.04 mg/kg) on two separate occasions, the mean +/- s.e. mean exercise heart rate rose by 10.3 +/- 1.8 beats/min and by 11.0 +/- 1.6 beats/min respectively. This increase was designated the 'vagal effect and was not significantly different in the two studies. After atropinsation, propranolol (0.2 mg/kg) reduced mean +/- s.e. mean exercise heart rate by 45.3 +/- 2.6 beats/min and 0.4 mg/kg by 50.8 +/- 4.5 beats/min. This mean sympathetic blockade was not altered significantly by increasing the dose of propranolol but, in four of the six subjects, the larger dose produced an increased effect of 4, 6, 12 and 16 beats/min, suggesting that maximum sympathetic blockade may not have been produced by 0.2 mg/kg. Knowledge of the vagal effect in each subject with standardised exercise enabled prediction to be made of the exercise heart rate after propranolol (0.4 mg/kg) without previous atropinisation. Propranolol (0.4 mg/kg) was then given intravenously to each subject and the actual exercise heart rate measured. There was no significant difference between the predicted and observed exercise heart rates. Propranolol (0.6 mg/kg) without atropine was then given to the four subjects who had shown increased effect with (0.4 mg/kg) and the sympathetic blockade was measured. In one subject, a further increase in sympathetic blockade of 10 beats/min was found. The intrinsic heart rate at rest and on exercise was measured for propranolol (0.2 and 0.4 mg/kg) and, for propranolol (0.6 mg/kg), the intrinsic heart rate on exercise was calculated. At rest, although no significant difference was found between the two dose levels, three subjects did not appear to have maximum autonomic blockade at 0.2 mg/kg. Similarly, several subjects had lower intrinsic heart rates on exercise after 0.4 or 0.6 mg/kg than after 0.2 mg/kg. The intrinsic heart rate on exercise was significantly greater than that obtained at rest. Using the maximum sympathetic blockade obtained in each subject as the sympathetic component of exercise, the effects of increasing oral doses of practolol on exercise heart were measured as percentage blockade of sympathetic effect and this was compared with other conventional methods of measuring beta-adrenoceptor blockade. It was found that percentage blockade of sympathetic effect correlated most closely with both percentage and absolute reduction of exercise heart rate. Correlations with exercise heart rate after drug and percentage inhibition of tachycardia, whilst also significant, did not appear as good. When the effects of practolol were expressed in terms of the potential blockade, a plateau occurred between 70 and 80% of 'maximum' sympathetic blockade. The failure to achieve higher levels with practolol may be the result of its partial agonist or intrinsic sympathomimetic activity.

An investigation of the relationship between ?-adrenoceptor blockade and plasma practolol concentration in man

In a group of 12 healthy subjects, the relationship between β-blocking activity and plasma practolol concentration was studied at intervals up to 24 h after a single 200 mg oral dose of practolol and placebo. β-Blockade was assessed by measuring inhibition of exercise heart rate and FEV1, and the plasma practolol level was determined spectrophotometrically. Significant reduction in mean exercise heart rate was detected 1 to 24 h after practolol but there was no significant reduction in mean resting heart rate or FEV1. The plasma practolol elimination half life in 8 subjects gave a mean of 5.9 h. The ratio of exercise heart rate inhibition to log plasma practolol concentration increased during the first few hours.

Hemodynamic response to exercise after beta-adrenergic and parasympathetic blockade.

Cardiac responses to supine bicycle exercise were studied in six normal subjects after the intravenous administration of 5 mg of propranolol and again after the additive effect of 0.03 mg/kg of atropine. Mean resting heart rate was decreased 15 beats/min by propranolol and then increased by 38 beats/min after atropine. Mean exercise heart rate was 157 for control exercise, 119 after propranolol and 143 after propranolol + atropine. The resting cardiac index was reduced 21% by propranolol and restored to control values after atropine. The mean control exercise cardiac index was 7.2 l/min per m2; this was reduced to 5.8 after propranolol and increased to 6.2 after atropine. The mean stroke index was not altered by control exercise, increased 3 ml/beat per m2 with exercise after propranolol and increased 6 ml/beat per m2 with exercise after propranolol + atropine. Resting pulmonary artery, aortic and left-ventricular end-diastolic pressures were not altered by propranolol or by propranolol + atropine. The mean control exercise left-ventricular end-diastolic pressure was 9 mm Hg, increased to 19 mm Hg after propranolol and fell to 12 mm Hg after propranolol + atropine. The mean exercise aortic systolic pressure was 10 mm Hg below the value for control exercise after propranolol and 8 mm Hg below control after propranolol + atropine. Atropine lessens the inhibition of the cardiac response to exercise with beta adrenergic inhibition, possibly by increasing the heart rate.