Respiratory physiology & neurobiology
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Respir Physiol Neurobiol · Aug 2011
Compartmental chest wall volume changes during volitional normocapnic hyperpnoea.
During increased ventilation, inspiratory rib cage muscles have been suggested to take over part of diaphragmatic work after the diaphragm fatigues. We investigated the extent to which this proposed change in muscle recruitment is associated with changes in the relative contribution of chest wall compartments to tidal volume (V(T)). ⋯ While breathing frequency increased (43±3 to 56±5 breaths min(-1), p=0.006) and V(T) decreased during normocapnic hyperpnoea (2.6±0.2 to 1.9±0.1l, p<0.001), the relative contribution of chest wall compartments to V(T) remained unchanged (pulmonary rib cage: 48±9 versus 51±14%; abdominal rib cage: 24±4 versus 23±9%; abdomen: 28±8 versus 26±9%; all p>0.05). In conclusion, fatiguing respiratory work is not associated with a change in compartmental contribution to V(T), even in the presence of a change in breathing pattern.
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Respir Physiol Neurobiol · Aug 2011
Sex differences in exertional dyspnea in patients with mild COPD: physiological mechanisms.
The purpose of this study was to evaluate the physiological basis for sex-differences in exercise-induced dyspnea in patients with mild COPD. We compared operating lung volumes, breathing pattern and dyspnea during incremental cycling in 32 men (FEV(1)=86±10% predicted) and women (FEV(1)=86±12% predicted) with mild COPD and 32 age-matched controls. There were no sex differences in dyspnea in the control group at any work-rate or ventilation (V(E)). ⋯ At 80 W, dyspnea ratings were 5.7±2.3 and 3.3±2.5 Borg units (P<0.05) and the V(E) to maximal ventilatory capacity ratio was 72% and 55% in women and men, respectively (P<0.05). Comparable increases in dynamic hyperinflation were seen in both male and female COPD groups at symptom limitation but women reached tidal volume constraints at a lower work rate and V(E) than men. Superimposing mild COPD on the normal aging effects had greater sensory consequences in women because of their naturally reduced ventilatory reserve.
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Respir Physiol Neurobiol · Aug 2011
Alteration of carotid body chemoreflexes after neonatal intermittent hypoxia and caffeine treatment in rat pups.
In human neonates, caffeine therapy for apnoea of prematurity, especially when associated with hypoxemia, is maintained for several weeks after birth. In the present study, we used newborn rats and whole-body plethysmography to test whether chronic exposure to neonatal caffeine treatment (NCT), alone or combined with neonatal intermittent hypoxia (n-IH) alters: (1) baseline ventilation and response to hypoxia (12% O(2), 20 min); and (2) response to acute i.p. injection of caffeine citrate (20 mg/kg) or domperidone, a peripheral dopamine D2 receptor antagonist (1 mg/kg). Four groups of rats were studied as follows: raised under normal conditions with daily gavage with water (NWT) or NCT, or exposed to n-IH (n-IH+NWT and n-IH+NCT) from postnatal days 3 to 12. ⋯ During the late response phase to hypoxia (20 min), ventilation was lower in n-IH+NWT and n-IH+NCT rats compared to NWT or NCT, and were not affected by caffeine or domperidone injection. NCT or caffeine injection decreased baseline apnoea frequency in all groups. These data suggest that chronic exposure to NCT alters both carotid body dopaminergic and adenosinergic systems and central regulation of breathing under baseline conditions and in response to hypoxia.
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Respir Physiol Neurobiol · Jul 2011
Altered ventilatory and thermoregulatory control in male and female adult Pet-1 null mice.
The integrity of the serotonin (5-HT) system is essential to normal respiratory and thermoregulatory control. Male and female transgenic mice lacking central 5-HT neurons (Lmx1b(f/f/p) mice) show a 50% reduction in the hypercapnic ventilatory response and insufficient heat generation when cooled (Hodges and Richerson, 2008a; Hodges et al., 2008b). Lmx1b(f/f/p) mice also show reduced body temperatures (T(body)) and O(2) consumption [Formula: see text] , and breathe less at rest and during hypoxia and hypercapnia when measured below thermoneutrality (24 °C), suggesting a role for 5-HT neurons in integrating ventilatory, thermal and metabolic control. ⋯ In addition, V(E) and [Formula: see text] were decreased in male and female Pet-1 null mice during hypoxia and hypercapnia (P < 0.05), but only male Pet-1 null mice showed a significant deficit in the hypercapnic ventilatory response when expressed as % of control (P < 0.05). Finally, male and female Pet-1 null mice showed significant decreases in T(body) when externally cooled to 4 °C. These data demonstrate that a moderate loss of 5-HT neurons leads to a modest attenuation of mechanisms defending body temperature, and that there are gender differences in the contributions of 5-HT neurons to ventilatory and thermoregulatory control.
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Respir Physiol Neurobiol · Apr 2011
Cartography of human diaphragmatic innervation: preliminary data.
In humans, anatomy indicates that the phrenic nerve mainly arises from the C4 cervical root, with variable C3 and C5 contributions. How this translates into functional innervation is unknown. The diaphragm response to electrical stimulation of C3, C4 and C5 was described in three patients undergoing surgical laryngeal reinnervation with an upper phrenic root (surface chest electrodes at anterior, lateral and posterior sites; oesophageal and gastric pressures (Pes and Pga) to derive transdiaphragmatic pressure (Pdi)). ⋯ It produced Pdi values of 9, 11, and 14cmH(2)O in the three patients, respectively, vs. 9, 9, and 7cmH(2)O for C4. C3 stimulation produced modest Pdi responses, whereas C5 stimulation could produce Pdi responses close to those observed with C4 stimulation. These singular observations confirm the dominance of C4 in diaphragm innervation but suggest than C5 can be of importance.