THE EFFECT OF POSTURE UPON THE COMPOSITION AND VOLUME OF THE BLOOD IN MAN 1

Abstract

The microhematocrit (HCT) values of 59 subjects increased significantly in the sitting position and after moderate exercise, in comparison with the values obtained during recumbency. The consumption of an 800-calorie meal decreased the HCT and this effect lasted for six hours. In order to obtain comparable results blood for HCT should be taken in a "standard basal con¬ dition" in the morning hours, in the fasting state or after a light breakfast, and the patient should sit for at least 30 minutes before the blood specimen is taken. rT,HE high reproducibility and accuracy of ¦¦¦ hematocrit determinations have made this test very useful and popular in routine laboratory studies. The individual hematocrit values of healthy subjects and of patients without obvious disorders of plasma or red cell volume are considered in recent textbooks as constant during a period of one or several days. A few publications in the past, however, demonstrated some diurnal, post¬ prandial and postural changes in red blood cell count, hemoglobin and hematocrit values.16 Since the stability or fluctuation of hematocrit value, independent of any morbid condition in healthy or sick individuals, is of practical importance, we investigated this problem in 59 volunteers. Material This study was carried out on 31 healthy (H) hospital employees (six females and 25 males) and on 28 patients (eight females and 20 males) with chronic coronary heart disease (CHD). The healthy subjects performed light hospital duties involving moderate physical activity. Most of the patients were hospitalized in the Special Investiga¬ tion Unit for reassessment of their condition. All were ambulatory, without acute distress, heart failure or hypertension, and did not take drugs except for nitroglycerin occasionally; 22 of the pa¬ tients were on long-term anticoagulant therapy during this study. During the testing periods they did not have anginal episodes and did not take nitroglycerin. Several volunteers participated in more than one experiment described in this study. SOMMAIRE Les valeurs de la microhematocritie (HCT) de 59 sujets ont augmente sensiblement en position assise et apres un exercise modere, par rapport aux chiffres fournis alors que les sujets etaient couches. La consommation d'un repas de 800 calories a diminue' la valeur de 1*HCT et cet effet a persist£ pendant six heures. En vue d'obtenir des resultats comparables, le sang destme1 a FHCT doit 6tre preleve "dans des condi¬ tions de base standards", aux heures du matin, a jeun ou apres un leger petit dejeuner et le malade devrait etre assis pen¬ dant au moins 30 minutes avant de prelever le specimen de sang. Unless stated otherwise the volunteers walked to the laboratory and were seated for at least 30 minutes before tests. The withdrawal of blood was carried out with the subject in sitting position, the arm being approximately at the level of the heart. For tests during recumbency the blood was taken from volunteers resting in their beds. Method Ten ml. of blood was drawn through a 19-gauge needle from the antecubital vein in a dry syringe after application of a tourniquet for no more than 15 seconds and transferred to a Vacutainer tube containing 10 units of dry heparin per ml. of blood. The tube was placed in a slowly rotating mixer for 10 to 20 minutes to prevent sedimentation of the cellular elements. Duplicate microhematocrit de¬ terminations (HCT) were performed immediately after this mixing period in a high-speed Drummond centrifuge, according to the technique of Strumia, Sample and Hart.7 The data presented in Tables I to VI represent the mean and standard deviation (SD) of the individual readings. Results 1. The reproducibility of the technique was evaluated by 20 tests made by five technicians upon the same blood sample. The mean value was 45.97%, SD ± .403, SE ± 0.09. (This last figure is the standard error of the technique.) 2. Diurnal variations were tested in 10 volunteers during their normal daily activities and in six subjects at complete bed rest. All these subjects were fasting throughout the experiment. Blood samples were taken at 9 a.m., at 12 noon and at 5