Taneja I, Moran C, Medow MS, Glover JL, Montgomery LD, Stewart JM. Differential effects of lower body negative pressure and upright tilt on splanchnic blood volume. Am J Physiol Heart Circ Physiol 292: H1420 -H1426, 2007. First published November 3, 2006; doi:10.1152/ajpheart.01096.2006.-Upright posture and lower body negative pressure (LBNP) both induce reductions in central blood volume. However, regional circulatory responses to postural changes and LBNP may differ. Therefore, we studied regional blood flow and blood volume changes in 10 healthy subjects undergoing graded lower-body negative pressure (Ϫ10 to Ϫ50 mmHg) and 8 subjects undergoing incremental head-up tilt (HUT; 20°, 40°, and 70°) on separate days. We continuously measured blood pressure (BP), heart rate, and regional blood volumes and blood flows in the thoracic, splanchnic, pelvic, and leg segments by impedance plethysmography and calculated regional arterial resistances. Neither LBNP nor HUT altered systolic BP, whereas pulse pressure decreased significantly. Blood flow decreased in all segments, whereas peripheral resistances uniformly and significantly increased with both HUT and LBNP. Thoracic volume decreased while pelvic and leg volumes increased with HUT and LBNP. However, splanchnic volume changes were directionally opposite with stepwise decreases in splanchnic volume with LBNP and stepwise increases in splanchnic volume during HUT. Splanchnic emptying in LBNP models regional vascular changes during hemorrhage. Splanchnic filling may limit the ability of the splanchnic bed to respond to thoracic hypovolemia during upright posture.vasoconstriction; splanchnic; blood volume; orthostatic stress; hemorrhage STANDING TRANSLOCATES BLOOD from the central thoracic circulation to the dependent regional circulations, producing ϳ20% reduction in cardiac output. The decrease in cardiac output comprises a 40% decrease in stroke volume associated with reflex tachycardia, increased peripheral resistance, and a generally maintained systolic blood pressure (SBP) with somewhat reduced pulse pressure (PP) while quietly standing (35). Changes in circulatory physiology during head-up tilt (HUT) are said to resemble the changes observed during hypovolemia caused by dehydration or hemorrhage (39, 41).Lower body negative pressure (LBNP; see Refs. 44 -46) has been used as a reversible simulation for hemorrhage (8,30). LBNP has also been used to model orthostatic stress (7) because many of the changes of neurovascular physiology resemble changes during standing or HUT (31). Thus, for example, both HUT and LBNP produce central hypovolemia and comparable unloading of the cardiopulmonary and arterial baroreceptors (9, 19). However, gravitational differences in regional vascular properties have also been noted (21, 24). Thus recent work by Cooke et al. (8) and el Bedawi and Hainsworth (12) has demonstrated that, although LBNP physiology most closely resembles the physiology of acute hemorrhage, it may be incomplete as a model for orthostatic stress, which must prod...

SummaryIncidence rates of electrocardiographic changes during Caesarean section vary from 25 to 60%. To date, no investigator has identified myocardial ischaemia resulting from these changes. We investigated patients undergoing elective Caesarean section using peripartum Holter monitoring and serum analysis of cardiac troponin I (cTnI). Twenty-six patients presenting for elective Caesarean section were studied. Peroperative Holter monitoring continued for 12 h postoperatively, at which time blood samples for cTnI levels were taken. Significant ST changes were recorded in 42% of patients peroperatively and 38.5% of patients postoperatively. Forty-two per cent of patients experienced peroperative chest pain requiring opioid analgesia. Chest pain was significantly associated with abnormal electrocardiogram (ECG) findings. Ischaemic levels of cTnI were recorded in two patients. This study reports, for the first time, myocardial ischaemia (7.69% of patients) arising in conjunction with the ECG changes seen during elective Caesarean section. We also report episodes of significant postoperative ST-segment changes.

We conclude that there is a direct correlation between the incidence of epidural vein cannulation and patient posture during epidural catheter insertion in parturients.

Incidence rates of electrocardiographic changes during Caesarean section vary from 25 to 60%. To date, no investigator has identified myocardial ischaemia resulting from these changes. We investigated patients undergoing elective Caesarean section using peripartum Holter monitoring and serum analysis of cardiac troponin I (cTnI). Twenty-six patients presenting for elective Caesarean section were studied. Peroperative Holter monitoring continued for 12 h postoperatively, at which time blood samples for cTnI levels were taken. Significant ST changes were recorded in 42% of patients peroperatively and 38.5% of patients postoperatively. Forty-two per cent of patients experienced peroperative chest pain requiring opioid analgesia. Chest pain was significantly associated with abnormal electrocardiogram (ECG) findings. Ischaemic levels of cTnI were recorded in two patients. This study reports, for the first time, myocardial ischaemia (7.69% of patients) arising in conjunction with the ECG changes seen during elective Caesarean section. We also report episodes of significant postoperative ST-segment changes.

No abstract