Near-infrared monitoring of tissue oxygenation during application of lower body pressure at rest and during dynamical exercise in humans.

During the application of a wide range of graded lower body pressures (LBP) (-50 to 50 mmHg), we examined how (1) the tissue oxygenation in the lower and upper parts of the body changes at rest, and (2) how tissue oxygenation changes in the lower extremities during dynamical leg exercise. We used near-infrared spectroscopy (NIRS) to measure the changes induced by LBP in total Hb content and Hb oxygenation in seven subjects. At rest, total Hb increased and Hb oxygenation decreased in the thigh muscles during -25 and -50 mmHg LBP, while both decreased during +25 and +50 mmHg LBP. However, in the forearm muscles during graded LBP, the pattern of change in total Hb was the reverse of that in the thigh. Measurements from the forehead showed changes only during +50 mmHg LBP. These results demonstrated that the pattern of change in total Hb and Hb oxygenation differed between upper and lower parts with graded LBP at rest. During dynamical leg exercise, total Hb and Hb oxygenation in the thigh muscles decreased during stepwise increases in LBP above -25 mmHg, Hb oxygenation decreasing markedly during +50 mmHg LBP. These results suggest that during dynamical exercise (i) LBP at +25 mmHg or more causes a graded decline in blood volume and/or flow in the thigh muscles, and (ii) especially at +50 mmHg LBP, the O2 content may decrease markedly in active muscles. Our results suggest that NIRS can be used to monitor in a non-invasive and continuous fashion the changes in oxygenation occurring in human skeletal muscles and head during the graded changes in blood flow and/or volume caused by changes in external pressure and secondary reflexes both at rest and during dynamical exercise.

Differences in regional sweating responses during exercise between athletes trained on land and in water.

We investigated whether there are any differences in regional sweating responses during exercise between athletes trained on land and in water. We measured the local sweating rates on the left forearm (mswf) and the left scapula (msws), body temperatures (mean skin temperature, and rectal temperature Tre) in eight athletes trained on land (five soccer players, one distance runner and two baseball players, L group) and seven athletes trained in water (seven swimmers, W group) during cycle ergometer exercise at 50% maximal oxygen uptake for 40 min. The heart rate and oxygen uptake in the two groups during exercise showed nearly the same pattern of change. The Tre at the end of the exercise were 38.13 (SEM 0.19) degrees C in the L group and 38.26 (SEM 0.34) degrees C in the W group. Although the mswf in the two groups were similar, msws were significantly higher in L than in W at 30, 35 and 40 min of exercise. The msws at any given mean body temperature tended to be greater in L than in W. These results showed that a difference in regional sweating rate during exercise between the athletes trained on land and in water was present on the scapula.

Enhancement of parasympathetic cardiac activity during activation of muscle metaboreflex in humans.

We measured the changes in heart rate (HR) variability estimated from the standard deviation of the R-R intervals to evaluate cardiac parasympathetic tone noninvasively before and during activation of muscle metaboreflex induced by postexercise muscle ischemia. Eight healthy male subjects performed sustained handgrip at 50% maximal voluntary contraction followed by forearm occlusion. Mean arterial pressure, cardiac stroke volume, and ratio of cardiac preejection period to left ventricular ejection time (PEP/LVET) were also measured. During the 2-min occlusion after 60 s of handgrip with voluntary respiration, HR variability and mean arterial pressure were significantly increased from baseline (54.4 +/- 6.1 to 80.1 +/- 12.8 ms and 81 +/- 1 to 99 +/- 3 mmHg, respectively) and PEP/LVET was decreased from resting level of 0.404 +/- 0.022 to 0.363 +/- 0.036. During occlusion and recovery, HR did not change from baseline level in any experiment. There was no influence of occlusion itself or of cessation of exercise per se on any parameters. Although overall enhanced HR variability was seen, probably due to lower breathing frequency and larger tidal volume, similar results were also obtained from an experiment with controlled respiration, showing that the increase in HR variability was not due to the changes in tidal volume or breathing frequency during occlusion. In conclusion, the HR variability is increased during activation of the muscle metaboreflex induced by postexercise muscle ischemia in humans. This finding shows that the parasympathetic cardiac tone is enhanced during activation of the muscle metaboreflex in humans and balances enhanced cardiac sympathetic activity to result in an unchanged HR.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between mean arterial pressure and muscle cell pH during forearm ischaemia after sustained handgrip.

Recent evidence suggests that there is a close correlation between the physiological responses to muscle chemoreflex and the decrease in intracellular pH during ischaemia after handgrip. This study evaluated whether the relationship is linear or has an apparent threshold. We measured muscle cellular pH through phosphorous nuclear magnetic resonance spectroscopy (31P-NMR), mean arterial blood pressure (MAP) and heart rate (HR) during ischaemia after sustained handgrip exercise at 50% of maximum voluntary contraction (MVC). Contraction was sustained for 15, 30, 45 and 60 s, followed by 2 min of circulatory arrest, respectively. Muscular pH during the ischaemia decreased linearly with increasing contraction time, from the base-line level of 7.11 +/- 0.03 units (U) to 6.98 +/- 0.03, 6.90 +/- 0.04, 6.72 +/- 0.06 and 6.54 +/- 0.06 U after 15-, 30, 45-, and 60-s contractions, respectively. The MAP was 86 +/- 2 mmHg at rest and did not change during the ischaemia after 15- and 30-s contractions. However, it significantly increased to 95 +/- 2 and 107 +/- 2 mmHg, after 45- and 60-s contractions, respectively. These data indicate that the relationship between MAP and pH is not a single linear relationship, showing one breaking point around the pH of 6.90 units. It suggests that the muscle chemoreflex has a clear threshold around 6.90 units of muscle pH, and below this pH, MAP increased linearly with decreasing muscle cellular pH.

Truncated forms of mannose-binding protein multimerize and bind to mannose-rich Salmonella montevideo but fail to activate complement in vitro.

Human serum (MBP) and human recombinant (rMBP) mannose-binding protein bind to mannose-rich, serum-resistant Salmonella montevideo (SH5770), enhance C3 deposition, and render the organisms serum-sensitive. We investigated structural features of MBP necessary for this effect. MBP has a cysteine-rich amino-terminal region, a collagen-like region, and a carboxyl-terminal carbohydrate-recognition domain. We prepared carbohydrate-recognition domains lacking the other two domains either by deletion mutagenesis (delta MBP, 16 kDa) or by collagenase digestion of whole rMBP (cdMBP, 16-18 kDa). Whole and truncated MBP were detected on immunoblot by specific monoclonal antibodies that recognize both bound and free MBP. rMBP enhanced C3 deposition on SH5770 8-fold, while cdMBP and delta MBP did not increase C3 deposition over control levels. All forms of MBP bound to SH5770 by enzyme-linked immunosorbent assay and by measuring binding of radiolabeled whole and truncated MBP. Binding by 125I-delta MBP was inhibited by mannan and by MBP. Thus failure of truncated MBPs to enhance C3 deposition was not due to failure to specifically bind carbohydrate residues. To determine the molecular form of truncated MBP in nondenaturing conditions, 125I-delta MBP was centrifuged through a 5-20% sucrose-density gradient. The peak of 125I-delta MBP sedimented to estimated S20,w 2.01, but larger multimers also were present. Multimers bound SH5770 with higher affinity than monomers. We conclude that carbohydrate-recognition regions of MBP produced by collagenase digestion or by deletion mutagenesis are sufficient for ligand binding. However, the collagen-like region is necessary for MBP enhancement of C3 deposition on SH5770.

Sub-minimal inhibitory concentrations of cefmetazole enhance serum bactericidal activity in vitro by amplifying poly-C9 deposition.

Serum-resistant organisms grown in sub-minimal inhibitory concentrations (subMICs) of antibiotics in vitro may be rendered sensitive to complement-mediated, serum bactericidal activity. We measured 125I-C3 and 125I-C9 deposition on genetically serum resistant Salmonella montevideo SH5770 (SH5770) that was rendered serum sensitive by growth in sub-MICs of cefmetazole (CMZ), a parenteral, second generation, cephamycin-group antibiotic. Three times as much C3 and over six times as much C9 bound to SH5770 grown in one-fourth the MIC of CMZ compared to broth-grown bacteria. SDS-PAGE analysis and autoradiography showed that neither the ratio of C3b:iC3b (approximately 1:2.5) nor the nature of the C3-bacterial bond was changed by growing the organisms in CMZ. Large amounts of complement membrane attack complexes containing poly-C9 were seen only on CMZ-grown SH5770 by SDS-PAGE and autoradiography. Poly-C9 was also detected only on CMZ-grown bacteria by indirect immunofluorescence and ELISA using a murine monoclonal antibody directed against a neoantigen of poly-C9. Bacterial hydrophobicity increased after growth in CMZ, and transmission electron micrographs of CMZ-grown SH5770 showed cell wall disruption and blebbing. These results indicate that growth in subMICs of CMZ increases bacterial hydrophobic domains available for interacting with the membrane attack complex, C5b-9, allowing formation and stable insertion of bactericidal complexes containing poly-C9.