BRONCHIAL BLOOD FLOW AFFECTS PARTICLE CLEARANCE FROM SHEEP LUNGS 
Is mucociliary clearance of inhaled particles influenced by bronchial
blood flow? Wagner and Foster (p. 1878) measured the clearance of
labeled inert colloid aerosol particles (2.1-µm diameter) from the
lungs of anesthetized sheep under different conditions of bronchial
blood flow. One hour after aerosol deposition, particle retention was
~55% with normal bronchial blood flow but ~76% when bronchial
perfusion was stopped. Thus particle clearance was impaired by the
reduction in blood flow. Factors that may account for this influence
include the effects of bronchial blood flow on airway cell nutrition,
on temperature and humidity of the airway wall and its secretions, and
on the release of mediators.
COCA CHEWING AND HYPOXIC EXERCISE
The chewing of coca leaves to prevent fatigue is a widespread practice
among Andean people performing heavy work at high altitude. Favier et
al. (p. 1901) made metabolic and endocrine measurements in normal
subjects who denied habitual coca use during exercise in La Paz,
Bolivia (altitude 3,600 m) with and without 1 h of coca chewing just
before the exercise. Coca chewing increased heart rate and
O2 consumption during standardized
exercise, but the results provide no evidence that coca could enhance
exercise tolerance in nonhabitual users. In contrast, a previous study by the same workers showed that in habitual coca chewers acute coca use
led to an exaggerated rise in plasma epinephrine and increased free
fatty acid availability. Thus chronic coca use appears to alter the
response to an acute dose under these conditions.
DOES LOW BAROMETRIC PRESSURE CONTRIBUTE TO ACUTE MOUNTAIN SICKNESS?
Although most of the physiological consequences of exposure to high
altitude result from the low inspired
PO2, there are persistent suggestions
that the low barometric pressure may play an
O2-independent role. Roach et al.
(p. 1908) studied the development of symptoms of acute mountain
sickness in human volunteers exposed on three different days to
simulated altitude (4,564 m) and to equivalent degrees of normobaric
hypoxia and normoxic hypobaria. Symptom scores were highest in the
simulated altitude exposures. Low pressure alone did not induce
symptoms, but normobaric hypoxia produced significantly lower symptom
scores than did hypobaric hypoxia. The results suggest a small
contribution of low barometric pressure to the development of acute
mountain sickness symptoms during exposure to high altitude.
GENDER DIFFERENCES IN THE CONTROL OF BREATHING
Systemic administration of aspartic acid decreases ventilation in male,
but not female, rats, presumably by acting on
N-methyl-D-aspartate (NMDA) receptors. To begin to elucidate this finding, Schlenker (p.
1911) measured ventilation and metabolic rate in awake rats treated
with dextromethorphan (Dex), a noncompetitive NMDA-receptor antagonist.
Pretreatment with Dex did not influence ventilation in male rats but
prevented the reduction in ventilation by subsequent aspartic acid
administration. In contrast, Dex administration reduced ventilation in
female rats. These confusing results were complicated further by
Dex-induced reductions in O2
consumption in both genders and by hypercapnic ventilatory responses
that were reduced in females and increased in males. The
gender-specific ventilatory actions of Dex were not closely related in
time with the effects on metabolic rate.
DOES INCREASED CAPILLARY PERMEABILITY CONTRIBUTE TO
HIGH-ALTITUDE PULMONARY EDEMA?
The pathophysiology of high-altitude pulmonary edema is poorly
understood. Kleger et al. (p. 1917) approached the problem by asking
whether increased pulmonary capillary permeability might, in
susceptible individuals, reflect a generalized inflammatory response to
hypoxia and thus be associated with increased permeability of systemic
capillaries as well. In a study of 24 subjects exposed to an altitude
of 4,559 m, the investigators found no significant difference in
transcapillary escape of labeled albumin between four subjects who
developed pulmonary edema and other subjects who did not. The results
argue against a dominant role for a generalized increase in capillary
permeability in the pathogenesis of high-altitude pulmonary edema.
DEVELOPMENT OF THE DIAPHRAGM IN HYPOTHYROID RATS
Hypothyroidism is known to alter the developmental transitions in
myosin heavy chain (MHC) isoform expression that normally occur in
skeletal muscle during the postnatal period. Sieck et al. (p. 1965)
examined these transitions in the diaphragms of rat pups made
hypothyroid by treatment with propylthiouracil and related the altered
developmental pattern of MHC isoform expression to changes in
mechanical performance. The diaphragms of propylthiouracil-treated rats
exhibited reduction in maximal force development, unloaded shortening
velocity, and fatigability. The authors suggest that some, but not all,
of these abnormalities are attributable to changes in MHC isoform
expression.
COORDINATION AND LEARNING IN STRENGTH TRAINING
Some reports suggest that muscle training programs are most effective
in increasing performance when the performance is assessed at or near
the contractile velocity used in the training program. Almåsbakk
and Hoff (p. 2046) investigated this velocity specificity of training
by examining strength gains in the context of learning a new skill.
Young women with no previous strength training were instructed in
bench-press exercise, some with a heavy load and others with a very
light load. After 6 wk, only the group training with the heavy load
increased maximum strength, but both groups increased the maximum
velocity of contraction to the same extent and over a wide range of
loads. The findings suggest that early velocity-specific strength gains
in training programs with unfamiliar tasks may reflect increasing skill
and coordination rather than adaptations within the muscles.
ENDOTHELIAL VASODILATORS LINK SHEAR STRESS AND FLOW
DISTRIBUTION
Shear stress of the vascular wall is a known vasodilator
stimulus that requires intact endothelial cells to be effective. To
examine the role of this mechanism in the distribution of blood flow in
an intact arteriolar network, Frame and Sarelius (p. 2105) used a
hamster cremaster muscle preparation and measured cell flow, shear
stress, and bifurcation angles in four generations of microvessels.
Vasoconstriction by hyperoxia or norepinephrine resulted in coupled
changes in shear stress and cell flow, whereas vasoconstriction by
inhibition of endothelial synthesis of nitric oxide and prostacyclin
uncoupled shear stress and flow. The results suggest that flow
distribution is normally influenced by endothelial vasodilators
released by shear stress in intact vascular beds.
THE MENSTRUAL CYCLE INFLUENCES CARDIOVASCULAR RESPONSES TO
HYPERCAPNIA
Ventilation is slightly higher during the luteal phase of the
menstrual cycle than during the follicular phase, perhaps as a result
of ventilatory stimulation by progesterone. Edwards et al. (p. 2142)
investigated cardiovascular responses to acute hypercapnia in normal
women during both follicular and luteal phases. Systolic and diastolic
blood pressure increased more with hypercapnia during the luteal phase,
but the responses of heart rate did not vary with the menstrual cycle.
Serum progesterone was higher during the luteal than the follicular
phase, but the role of this hormone in the cardiovascular responses is
unclear.
REFLEX CONTROL OF CUTANEOUS VASODILATION
Crandall et al. (p. 2192) sought to determine whether reductions in
cutaneous active vasodilation during simulated orthostasis could be
caused solely by unloading either cardiopulmonary baroreceptors or
carotid baroreceptors. Lower body negative pressure of 
5 and 10 mmHg in hyperthermia, which decreased cardiopulmonary
baroreceptor discharge, did not change cutaneous vascular conductance
(CVC) but reduced forearm vascular conductance (FVC). Pulsatile carotid pressure of 45 mmHg, which decreased carotid baroreceptor discharge, had no effect on either CVC or FVC during hyperthermia or normothermia but increased heart rate and arterial pressure. The investigators conclude that selective unloading of either cardiopulmonary or carotid
baroreceptors cannot account for the reduction of cutaneous active
vasodilation seen during orthostasis.
BRONCHIAL BLOOD FLOW AFFECTS PARTICLE CLEARANCE FROM SHEEP LUNGS
