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JEPonline
Arm Position Affects Calculation of Posture-Induced Versus Jogging-Induced Plasma Volume Change
William Sullivanand Michele M. Fisher
Department of Exercise Science and Physical Education,Montclair State University, Montclair, NJ 07043 USA
ABSTRACT
Sullivan W, Fisher MM. Arm Position Affects Calculation of Posture-Induced Versus Jogging-Induced Plasma Volume Change.JEPonline2018;21(1):116-126. The effect of blood sampling arm position on the calculation of standing-induced versus jogging-induced change in plasma volume (∆PV) has not been determined. This study examined the effect of arm position on posture-inducedversus jogging-induced ∆PV. Eleven physically active men with a mean age of 25.7 ± 5.7 yrs lay supine for 30 min, stood upright for 30 min, and then jogged at ~75% of age-predicted maximal heart rate. During the standing rest and exercise, one arm was pendent (Pendent) while the other arm was supported in a position parallel to the floor (Horizontal). Blood was drawn from both arms at the end of the supine and standing rest periods and after ~12 min of exercise. There was an interaction (F1,10 = 10.373, P = 0.009, 2p = 0.509) between arm position and condition on ∆PV. Post hoc paired t tests revealed a greater ∆PV (t = 2.340, P = 0.041, ES = 1.02, 95% CI of mean difference = 0.23 to 9.57) in the Pendent arm (-12.9 ± 5.7 %) compared to the Horizontal arm (-8.0 ± 3.8 %) when going from a supine to standing position. Whensubjects switched from a standing condition to the jogging condition, PV was greater (t = -2.930, P = 0.015, ES = 1.37, 95% CI of mean difference = -12.53 to -1.71) in the Horizontal arm (-6.2 ± 5.5 %) compared to the Pendent arm (0.9 ± 4.8 %). There was no difference in ∆PV from the supine condition through the exercise bout (t = 0.223, P = 0.828, ES = 0.10, 95% CI of mean difference = -5.65 to 6.90) between the Pendent (±12.6 + 4.4%) and Horizontal (±12.0 + 8.2%) arm. Thus, blood-sampling arm position affects the calculation of posture-induced versus jogging-induced ∆PV and should be considered in the experimental design.
Key Words:Exercise, Hematocrit, Hemoglobin, Fluid Shifts
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INTRODUCTION
Plasma volume (PV) generally expands as a result of both chronic aerobic training (8,13,18,27) and high intensity interval training (3). The increase in PV as a result of chronic aerobic training results in a cascade of adaptations, including an increase in blood volume, venous return to the heart, and stroke volume with a concomitant decrease in heart rate (HR) at any given absolute workrate. Also, several studies have quantified the PV response to an acute bout of exercise in a thermoneutral environment. In studies that did not allow fluid intake during the experimental procedure, PV generally decreased as exercise intensity increased during upright cycling (15,18,29). However, there is disagreement on the effect of an acute bout of jogging/running on ∆PV. Some investigators have observed a decrease in PV (22,26,28) while others have found no ∆PV (11).
These discrepant findings may be explained by the influence of body posture versus arm position in which the pre-exercise control blood sample was drawn. Plasma volume generally decreases when subjects go from the supine position to the upright standing position (4,5,17). But few studies reporting the ∆PV during upright exercise differentiated between posture-induced vs. exercise-induced ∆PV and none reported the effect of blood-sampling arm position. Blood sampling arm position affects ∆PV when using ∆hematocrit (Hct) and/or ∆hemoglobin (Hb) to calculate ∆PV (10,15), which are the most common methods reported in the literature. Both Hct (12) and Hb (21) have been reported to be greater in a pendant arm hanging vertically at the subject’s side than an arm supported in the horizontal position when subjects stand upright.
In the studies examining ∆PV during jogging or running, only one study reported the position of the blood-sampling arm (11) after a pre-exercise seated control posture. Also, a recent study found an interaction between the blood sampling arm position and the condition such that ∆PV was greater in thePendent arm than in the arm supported in the Horizontal position when the subjects went from supine to seated rest. But, ∆PV was greater in the Horizontal arm than in the Pendent arm from seated rest through a bout of cycling, and yet the decrease in PV was similar in the Pendent arm and the Horizontal arm from the supine rest measure through the cycling bout (30). No study has examined the effect of arm position on calculation of posture-induced vs. exercise-induced ∆PV when subjects are moved from supine rest to the standing rest position and then from standing rest through a subsequent bout of jogging.
Therefore, the purpose of the present study was to determine the effect of arm position (Horizontal versus Pendent) on the calculation of posture-induced versus jogging-induced ∆PV from supine rest to standing rest, from standing rest through a bout of jogging, and from supine rest through the exercise bout.
METHODS
Subjects
Prior to participation in the experiment, 11 apparently healthy and physically active male undergraduate university students read and signed an informed consent approved by the university’s Institutional Review Board. The subjects also completed a medical history and physical activity history questionnaire. Any potential subject with a history of heart, vascular, pulmonary, thyroid, kidney, and/or liver disease or who had a history of hypertension or diabetes mellitus was excluded from the subject pool.
Procedures
The data were collected in the fall season in order to control for heat acclimation. Room temperature was 22.3 ± 0.3 °Cand relative humidity 49.9 ± 2.1 %, within a narrow range across all experiments. In order to prevent any effect of unaccustomed physical activity, each subject was asked to not participate in any physical activities for 3 d prior to the experiment getting underway. Also, each subject was instructed to not eat anything for 12 hrs prior to the experiment (all experiments were conducted in the early morning), but was encouraged to drink at least 1L of water the evening before the test and the morning of the test prior to arriving at the lab.
Upon arrival at the lab, urinary specific gravity (USG) was measured via refractometry (Reichert-Jung TS Meter Refractometer, Model # 10400A) to assess hydration status. If the USG reading was greater than 1.015, the subject drank 1 L of tap water (2,24). After ~30 min had passed, USG was measured again. Each subject who had an initial USG greater than 1.015 had achieved USG less than 1.015 after one attempt at rehydration. After euhydration was achieved, the subject’s height and body mass were assessed.
After the initial assessments were completed, the subject lay supine on an examining table for 30 min with both arms supported in the horizontal position (parallel to the floor). Then, the subject stood upright for 30 min with one arm in the pendent position next to his body (Pendent) and the other arm abducted at approximately 90°, resting on a pillow that was supported by a cart with the cubital vein at the level of the heart (Horizontal). A carpenter’s level was used to assess the level of the vein relative to the level of the heart. During the transition from supine to standing rest, the Horizontal arm was supported so that the cubital vein remained at approximately heart level. The subjects’ arm assignment (Pendent versus Horizontal) for this study was counterbalanced for arm dominance (dominant versus non-dominant).
After 30 min of quiet standing, the subject began walking on a motor driven treadmill at 3 kp·h-1 at 0 grade. The speed of the treadmill, but not the grade, was increased until the subject reached approximately 60 to 70% of his age-predicted (220 – age) maximal HR (HRmax). The workrate was further adjusted, if necessary, until the subject’s HR reached a steady-state of ~75% of age-predicted HRmax. After completion of the exercise bout, the subject performed an active cool down at a workrate of 3 kp·h-1. Heart rate was measured during each minute of exercise (Polar Heart Rate Monitor, Vantage XL).
Rating of perceived exertion (RPE) was assessed during the 10th min of jogging at the target HR (7). Throughout the standing rest and exercise periods, the Horizontal arm remained in the supported position on the cart. The Pendent arm hung vertically during standing rest. During exercise, the Pendent arm swung moderately in the sagittal plane in rhythm with the jogging cadence. Also, throughout the experiment, the subject was coached not to make an isometric contraction or make a fist with either hand.
Blood Sampling
A sterile intravenous catheter was inserted into the cubital vein of each arm during supine rest. A sterile 3-way stopcock was attached to each catheter. Blood was drawn from each arm at approximately the 30th minute of supine rest, at approximately the 30th-min of standing rest (1,17), and at ~12 min of jogging at the target HR (6,23).
The following blood-sampling procedures were carried out throughout the experiment: (a) ~2cc of blood was withdrawn, without stasis, and discarded to account for dead space; (b) a resting blood sample was drawn, without stasis; and (c) 1 to 2 cc of sterile (non-heparinized) normal saline was then introduced into the catheter to keep the vein patent. The subject continued to jog during the blood sampling period and the time lapse between blood samples from the Pendent arm and the Horizontal arm was ~90 sec. The order for blood sampling was counterbalanced for both dominant vs. non-dominant arm and Pendent versus Horizontal arm position.
Hemoglobin was determined in triplicate, via spectrophotometry (Milton Roy, Spectronic 20D), by use of a cyanomethemoglobin solution (Sigma Chemical #525-A). Hematocrit was performed immediately after data collection in quadruplicate via microhematocrit centrifuge (Clay Adams Triac Centrifuge, Model # 0200). No correction was made to Hct for trapped plasma, Fcell ratio, or peripheral sampling. It was assumed that red cell volume remained constant (15).
The mean Hb and mean Hct of each sample were used to calculate the ∆PV from supine rest to the standing rest, from standing rest through the exercise bout, and from the supine rest through the exercise bout. The following formula was used to determine percent change in PV (10,15):
% ∆PV = ( [ {(Hb1) (1-Hct2)} / {(Hb2) (1-Hct1)} ] -1 ) x 100
where Hb1 and Hct1 were the values of the control blood sample and Hb2 and Hct2 were the values of the experimental blood sample at any given stage of the protocol (i.e., supine to standing rest, standing rest through the exercise bout, and supine rest through the exercise bout).
Statistical Analyses
Descriptive statistics (mean ± SD) were computed for subject characteristics (age, USG, height, and body mass) and response to exercise (workrate, HR, percentage of age-predicted HRmax, total exercise time, and time at target HR). Two-way analyses of variance with repeated measures were used to determine the presence of significant interactions between the arm positions (Horizontal vs. Pendent) and conditions (supine, standing, and exercise) on ∆PV (2 x 2), Hct (2 x 3), and Hb (2 x 3). In the event of violation of sphericity on the Mauchley’s test, the Greenhouse-Geisser adjustment was employed to evaluate significance of the F ratio. When a significant interaction existed, post hoc paired t tests were used to determine significant differences between Horizontal and Pendent arm position for each condition, and effect size (ES) was calculated. When significant main effects for conditions or arm positions existed, post hoc pairwise comparisons were calculated using the Bonferroni correction. Confidence intervals (CI) for all t tests and pairwise comparisons are reported as the difference of the means. The SPSS Statistics 22.0 software program was used for all analyses, except the ES, which was calculated by hand with a pooled standard deviation. A type one error rate of α = 0.05 was set a priori to indicate statistical significance for all analyses. Data from previous work in our laboratory suggested a mean difference in ∆PV ranging from 9.2% to 11.9% with standard deviations extending from 7.7% to 9.3%. The power to detect an effect of this size with 11 subjects and α = 0.05 was determined to fall between 78% and 90%.
RESULTS
Mean age, USG, height, and body mass were 25.7 ± 5.7 yrs, 1.012 ±0.006, 176.2 ± 11.2 cm, and 85.6 ± 14.3 kg, respectively. The following mean values were noted during exercise: workrate = 7.8 ± 1.5 kph, HR = 148.2 ± 15.7 beatsmin-1, percentage of age-predicted HRmax = 76.3 ± 7.9%, RPE = 11.9 ± 3.0, and total exercise time = 23.6 ± 2.1 min. Mean time spent at the target heart rate before the initial blood sample was drawn was 11.9 ± 1.6 min.
Plasma Volume
There was an interaction (F1,10 = 10.373, P = 0.009, 2p = 0.509) in PV between arm position and condition (Figure 1). Post hoc paired t tests revealed a greater ∆PV (t = 2.340, P = 0.041, ES = 1.02, 95% CI of mean difference = 0.23 to 9.57) in the Pendent arm compared to the Horizontal arm when going from the supine to standing posture. In contrast, when subjects switched from the standing condition to the jogging condition, PV was greater (t = -2.930, P = 0.015, ES = 1.37, 95% CI of mean difference = -12.53 to -1.71) in the Horizontal arm compared to the Pendent arm. When calculated from the supine rest values, PV from the supine condition through exercise revealed no difference (t = 0.223, P = 0.828, ES = 0.10, 95% CI of mean difference = -5.65 to 6.90) between the Pendent and Horizontal arm position.
Figure 1. Cumulative Change in Plasma Volume from Supine Rest through the Exercise Bout for the Pendent vs. Horizontal Arm (Mean ± SD). There was an interaction between arm position and condition such that change in plasma volume was greater in the Pendent arm than the Horizontal arm from the supine rest period through the standing rest period, but greater in the Horizontal arm than the Pendent arm from the standing rest period through the exercise bout. * = P≤0.05 for Pendent versus Horizontal arm
Hematocrit
An interaction (F2,20 = 20.259, P<0.001, 2p = 0.670) was observed between arm position and condition for Hct (Figure 2). During the standing condition, Hct was greater (t = -4.734, P = 0.001, ES = -0.58, 95% CI of mean difference = -2.58 to -0.93) in the Pendent arm compared to the Horizontal arm. There was no difference in Hct between the two arm positions during supine rest (t = 0.379, P = 0.712, ES = 0.03, 95% CI of mean difference = -0.35 to 0.50) or exercise (t = 0.984, P = 0.348, ES = 0.08, 95% CI of mean difference = -0.30 to 0.77).
Figure 2. Horizontal vs. Pendent Arm Hematocrit Ratio during Supine Rest, Standing Rest, and Exercise (Mean ± SD). There was an interaction between arm position and condition such that hematocrit ratio was greater in the Pendent arm than the Horizontal arm at the end of the standing rest period. * = P≤0.05 for Pendent versus Horizontal arm.
Hemoglobin
There was no interaction (F2,20 = 1.617, P = 0.223, 2p = 0.139) between arm position and condition for Hb (Figure 3). However, there was a main effect of condition (F2,20 = 21.735, P<0.001, 2p = 0.685) such that, when averaged across arm positions, Hb increased from supine rest to standing rest (+0.9 g·dL-1, P = 0.001, 95% CI of mean difference = 0.39 to 1.46) and from supine rest through the exercise bout (+1.2 g·dL-1, P<0.001, 95% CI of mean difference = 0.72 to 1.66), but not standing rest to exercise (+0.3 g·dL-1, P = 0.574, 95% CI of mean difference = -0.32 to 0.94).
Figure 3. Horizontal vs. Pendent Arm Hemoglobin Concentration during Supine Rest, Standing Rest, and Exercise (Mean ± SD). There was a main effect of condition such that hemoglobin concentration increased from supine rest through the standing rest period and from supine rest through the exercise bout. # = P≤0.05 for supine rest versus other conditions
DISCUSSION
This study examined the influence of blood-sampling arm position on posture-induced versus jogging-induced calculation of ∆PV. Arm position affected the calculation such that ∆PV was greater for the Pendent arm than the Horizontal arm when the subjects moved from the supine rest to the standing rest, but was greater for the Horizontal arm than the Pendent arm when the subjects transitioned from the standing rest through the exercise bout. In addition, ∆PV was similar for both arm positions from supine rest through the exercise bout.
Posture
When the subjects moved from supine rest to the standing rest posture in the present study, ∆PV was greater in the Pendent arm than the Horizontal arm. This finding is in agreement with our previous work, which reported that ∆PV was greater in a Pendent arm than a Horizontal arm (30) when the subjects moved from the supine rest to seated rest. Although not measured in the present study, the difference in ∆PV due to change in posture may be explained by the difference in capillary hydrostatic pressure between the two arm positions. Regional capillary hydrostatic pressure increases when a limb is moved from the horizontal position to the pendent position (9,14). This greater regional pressure results in a concomitant filtration from the regional intravascular space to the interstitial space (14,16), which results in an increase in both Hct (12) and Hb (21).
In addition, the present study found a greater Hct in the Pendent arm than the Horizontal arm during standing rest. However, there was no difference in Hb between the arm positions during standing rest in the present study. Thus, when calculating ∆PV from ∆Hct and ∆HB, the ∆PV should be greater in the Pendent arm than the Horizontal arm when moving from the supine posture to the upright posture. Also, Lundvall and Bjerkhoel (21) observed that the pendent arm arterial Hb was similar to the horizontal arm venous Hb, but different fromthe pendent arm Hb, when subjects moved from the supine posture to the standing posture. This suggests that horizontal arm venous Hb more closely represents arterial Hb than does pendent arm Hb.
Exercise
When subjects transitioned from standing rest through the bout of jogging, ∆PV was greater in the Horizontal arm than the Pendent arm. This finding is in agreement with our earlier paper (30) that foundthe change in PV was greater in the Horizontal arm than in the Pendent arm when the subjects transitioned from upright seated rest through a bout of cycling. The present findings for the Pendent arm are also in agreement with the results of Edwards and Harrison (11), who found that PV decreased when the subjects moved from the seated position to the standing position, but PV did not decrease further during a bout of jogging. In that study, the blood sampling arm was in the pendent position during jogging, but arm position was not described for the standing control period.