DO O2-SENSING NEUROEPITHELIAL ENDOCRINE CELLS INFLUENCE AIRWAY SMOOTH MUSCLE TONE?

Excised guinea pig tracheal preparations develop a sustained smooth muscle tone when studied in 94% O₂. At a more physiological O₂ concentration, however (12% O₂), a more complex oscillating pattern of tone develops and is sustained for many hours. Skogvall et al. (p. 789) present evidence that the complex, oscillating tone is epithelium dependent and that it is strongly regulated by O₂-sensing neuroepithelial endocrine cells within the airway epithelium. The study is discussed in an Invited Editorial by Cutz and Jackson (p. 787).

	PATTERNS OF PULMONARY CAPILLARY PERFUSION

Given the importance of the regional relationship between alveolar capillary blood flow and alveolar ventilation, surprisingly little is known about the pattern of pulmonary blood flow at the individual alveolar level. Wagner et al. (p. 825) studied red blood cell traffic through subpleural pulmonary capillaries to determine the kinematics of pulmonary capillary blood flow. In the zone 2 lung, not all capillary segments contained red blood cells at the same time, and red cell flow switched repetitively among the capillary segments of a single alveolar facet. The total number of segments containing red blood cells also varied with time in a way that suggested a fractal switching pattern. Surprisingly, the perfusion patterns in adjacent alveolar facets were unrelated to each other. The authors speculate that these characteristics impart robustness to the perfusion of gas-exchange units.

	CREATINE INTAKE AND MUSCLE PERFORMANCE

Dietary creatine supplementation has been found to improve intermittent high-intensity exercise performance. Van Leemputte et al. (p. 840) report that creatine supplementation augmented the rate of muscle relaxation in protocols that required repetitive, high-intensity isometric elbow flexion by human subjects. Maximal isometric force production was not affected. The authors suggest that the ergogenic effects of short-term, high-dose creatine supplementation are related to an improvement in the ability of muscles to relax after intense contractile activity.

	EFFICIENT RESPONSE TO INSPIRATORY THRESHOLD LOADS

Yan and Bates (p. 874) examined the responses of healthy, awake human subjects to small inspiratory threshold loads (2.5-10 cmH₂O). These loads must be overcome by the inspiratory muscles before airflow can be initiated at the start of each breath. The subjects responded by increasing tidal volume without changing respiratory frequency or the duration of inspiratory effort. Thus mean inspiratory flow rate and ventilation increased, but the inspiratory duty cycle was not extendeda beneficial strategy for limiting the energy expenditure of the inspiratory muscles.

	DOES RACE AFFECT FATIGUE RESISTANCE?

African men from Kenya hold world records in running at 800 m, 3 km, and in the steeplechase. Ethiopian men hold records at 5 and 10 km and in marathon running. North African (Caucasoid-Berber) men from Morocco and Algeria hold the 1,500-m and 1-mile records, respectively. In a study of nine Black South African and eight Caucasian 10-km runners matched for maximal O₂ uptake, Weston and associates (p. 915) noted that Africans could maintain 88% of peak treadmill velocity with lower respiratory gas-exchange ratios, lesser blood lactate accumulation, and longer time to fatigue. These performance differences were associated with 50% greater quadriceps citrate synthase and 28% greater phosphofructokinase activities. Although the number of subjects was small and the results could have been influenced by unmeasured variables, the African and Caucasian runners in this study differed with respect to oxidative enzyme activity, rate of lactate accumulation, and the ability to sustain high-intensity endurance exercise.

	MECHANISM OF INTESTINAL REPERFUSION INJURY

Williams and co-workers (p. 938) examined the roles of the alternative and classic pathways of complement and IgM in a murine model of intestinal ischemia-reperfusion. Wild-type animals; mice deficient in complement factors C4, C3, or immunoglobulin; or wild-type mice treated with soluble complement receptor 1 were subjected to 40 min of jejunal ischemia and 3 h of reperfusion. Compared with wild types, knockout and treated mice had significantly reduced intestinal injury. When animals deficient in immunoglobulin were reconstituted with IgM, the degree of injury was restored to wild-type levels. The authors conclude that ischemiareperfusion injury is dependent on the classic complement pathway and IgM.

	RELEASE OF MARGINATED LEUKOCYTES DURING EXERCISE

Margination is the removal of leukocytes from the circulating blood by adherence to the endothelium of the microcirculation. In the lung, the marginated pool of neutrophils is made up preferentially of young cells having comparatively high levels of L-selectin and low levels of the integrin CD11b on their surfaces. Exercise releases marginated neutrophils into the circulation. Surprisingly, van Eeden et al. (p. 970) report that, in humans, the demarginating cells express lower levels of L-selectin and higher levels of CD11b than do their circulating counterparts. Thus exercise selectively releases older and partially activated cells from the marginated pool.

	MATURATION OF STRIDE DYNAMICS

Toddlers, by definition, have less steady gaits than older children or adults. Hausdorff and colleagues (p. 1040) studied gait dynamics in healthy children, 3-14 yr of age. Measurements of stride-to-stride variability were greatest in 3-4 yr olds, intermediate in 6-7 yr olds, and lowest in 11-14 yr olds, who displayed the adult pattern. The temporal organization of gait also matured with age. Although fundamental stride dynamics are established by the age of 4 yr, learning and maturation effects persist for several years, even after adjustment for height. The results suggest that childhood activity plays a role in gait maturation.

	BAROMETRIC PRESSURE ON MT. EVEREST

The PO₂ on the summit of Mt. Everest (altitude 8,848 m) is close to the lower limit for human survival. The PO₂ is determined by the barometric pressure, which is easier to measure under adverse conditions. West (p. 1062) reviews the original 1981 measurement of barometric pressure at the summit and reports and analyzes recent measurements made at the summit, on the South Col (7,986 m), and at several altitudes in the vicinity, recorded from weather balloons. The new data are in close agreement with one another and with the 1981 measurement, confirming that on typical climbing days in May and October the pressure at the summit is 251-253 Torr.

	WAVELET TRANSFORM FOR ANALYSIS OF HEART RATE VARIABILITY

Fourier transform is the most commonly used method to analyze heart rate variability. Nevertheless, this method is limited to analyzing stationary signals, whereas wavelet transform is not. Pichot et al. (p. 1081) compared in humans the yields of Fourier and wavelet transforms in analyzing heart rate variability during changes in autonomic input to the heart, induced by atropine and propranolol. They found that wavelet transform yielded significantly better quantitative analysis of heart rate variability than did Fourier transform.