Results

The Effect of Temperature Variations on Volume Pulse. The effects of cold and heat stress on peripheral circulation and heart rate is summarized in Figure 1 and Figure 2, respectively. When cold stress was applied to the forearm, mean pulse wave amplitude decreased by nearly 42 percent, while mean heart rate decreased by seven percent compared to values obtained at rest (Figure 1). Within two minutes of recovery, both cold-induced increases returned to baseline levels. Variations in changes in R-pulse interval throughout the exposure and recovery periods were negligible since only slight changes (<5 percent) were verified. This treatment provided no significant changes to cardiovascular responses.

Figure 1. The effect of cold stress on heart rate () (BPM), plethysmographic pulse wave amplitude () (volts×102), and R-pulse interval () (seconds×102) in human cardiovascular response. No significant differences at 95% were noted in all three intervals analyzed using Student’s t-test. Values are the means of n=7 determinations ± standard error. Note: Significance testing was only performed on values obtained at rest versus 1 minute into recovery.

When heat stress was applied to the forearm, mean pulse wave amplitude significantly increased (P=0.001) by 249 percent, while heart rate significantly increased (0.017) by 19 percent, compared to values obtained at rest (Figure 2). Within two minutes of recovery, both heat-induced increases returned to baseline levels. Moreover, heat stress also significantly decreased R-pulse frequency (P=0.033) from 0.2388 ± 0.0147 seconds to 0.1444 ± 0.0357 seconds, following one minute of exposure. Similar to pulse wave amplitude and heart rate, R-pulse frequency gradually returned to baseline levels after two minutes of recovery.

Figure 2. The effect of heat stress on heart rate () (BPM), plethysmographic pulse wave amplitude () (volts×102), and R-pulse interval () (seconds×102) in human cardiovascular response. Significant differences at 95% were noted in all three intervals documented using Student’s t-test. Values are the means of n=7 determinations ± standard error. Note: Significance testing was only performed on values obtained at rest versus 1 minute into recovery.

ECG and Volume Pulse after Leg Exercise. Changes in parameters of cardiovascular response evoked by performing a leg exercise are expressed in Table 1. Immediately after performing linear jumps or walking stairs for three minutes, significant changes were observed in beat period, heart rate, R-wave amplitude, P-R interval, Q-T complex, T-P interval, and R-pulse interval, compared to data obtained at rest (baseline). At zero recovery, heart rate significantly increased (P≤0.001) by 64 percent. Although heart rate gradually started to decline, it remained 21 percent higher than values recorded at baseline after a 150 second rest period, thus exerting a profound effect on blood circulation. This trend was also observed in all eight parameters recorded, indicating that a recovery period longer than 150 seconds is required to return values back to baseline levels. Moreover, immediately after the exercise session, the remaining parameters showed significant decreases (range, 16–56 percent). The most profound decrease was the mean R-wave amplitude, declining from 0.7656 ± 0.0542 volts to 0.6097 ± 0.0392. No significant changes were noted in the results of pulse wave amplitude.

Table 1. The effect of leg exercise on various cardiovascular response parameters after jumping up vertically or walking stairs for three minutes. 

ECG and Volume Pulse after Hand Exercise. Changes in parameters of cardiovascular response evoked by squeezing a hand dynamometer are expressed in Table 2. Immediately after performing this exercise, significant changes were noted in beat period, heart rate, R-pulse interval, and R-wave amplitude, compared to data obtained at rest. At zero recovery, heart rate significantly increased (P=0.009) by 15 percent. Like the effects observed when jumping, heart rate gradually decreased beyond time zero recovery, but remained nearly ten percent higher than values recorded at baseline, thus exerting a profound effect on blood circulation. This trend was also evident in the three other parameters which showed significance, indicating that a recovery period longer than 150 seconds is required to return values back to baseline levels. Moreover, immediately after the exercise session, the remaining parameters showed significant decreases (range, 9–39 percent).

Table 2. The effect of hand exercise on various cardiovascular response parameters after rhythmically squeezing a dynamometer for three minutes.

The most profound decrease, aside from beat period, was the mean R-pulse interval, declining from 0.3066 ± 0.0914 seconds to 0.1868 ± 0.0146 seconds. No significant changes were noted in the results of pulse wave amplitude.

Table 3. The effect of caffeine ingestion (100 mg) contained in coffee beverage on cardiovascular responses.

ECG and Volume Pulse after Coffee Consumption. The effects of caffeine ingestion contained in coffee on peripheral circulation and heart rate is summarized in Table 3. Upon consuming the 250 ml cup of coffee, heart rate (88.0 ± 8.7321) increased by 34 percent to 118.0 ± 6.0817. On the contrary, beat period, pulse wave amplitude, and R-pulse interval decreased. Aside from beat period, the greatest magnitude of decrease was observed in pulse wave amplitude, declining from 0.1503 ± 0.0028 volts to 0.1045 ± 0.0104 seconds (30 percent). This data shows a similar pattern to what was observed when heat stress was applied to the forearm.