Breathing Rate (breathing + rate)

Distribution by Scientific Domains

Selected Abstracts

Factors affecting the deposition of inhaled porous drug particles

Cynthia J. Musante
Abstract Recent findings indicate that the inhalation of large manufactured porous particles may be particularly effective for drug delivery. In this study, a mathematical model was employed to systematically investigate the effects of particle size, particle density, aerosol polydispersity, and patient ventilatory parameters on deposition patterns of inhaled drugs in healthy human lungs. Aerodynamically similar particles with densities of 0.1, 1.0, and 2.0 g/cm3 were considered. Particle size distributions were defined with mass median aerodynamic diameters (MMADs) ranging from 1 to 3 ,m and geometric standard deviations ranging from 1.5 to 2.5, representing particles in the respirable size range. Breathing rates of 30 and 60 L/min with tidal volumes of 500 to 3000 mL were assumed, simulating shallow to deep breaths from a dry powder inhaler. Particles with a high density and a small geometric diameter had slightly greater deposition fractions than particles that were aerodynamically similar, but had lower density and larger geometric size (typical of manufactured porous particles). This can be explained by the fact that particles with a small geometric diameter deposit primarily by diffusion, which is a function of geometric size but is independent of density. As MMAD increased, the effect of density on deposition was less pronounced because of the decreased efficiency of diffusion for large particles. These data suggest that polydisperse aerosols containing a significant proportion of submicron particles will deposit in the pulmonary airways with greater efficiency than aerodynamically similar aerosols comprised of geometrically larger porous particles. © 2002 Wiley-Liss Inc. and the American Pharmaceutical Association J Pharm Sci 91:1590,1600, 2002 [source]

Relationship between breathing and cardiovascular function at rest: sex-related differences

B. G. Wallin
Abstract Aim:, To compare relationships at rest between breathing rate, levels of muscle sympathetic nerve activity, total peripheral resistance and cardiac output among young men and women. Methods:, Recordings were made of respiratory movements, sympathetic nerve activity (peroneal microneurography), intra-arterial blood pressure, electrocardiogram, cardiac output (open-circuit acetylene uptake technique) in 19 healthy men (age 27 ± 2 years, mean ± SEM) and 17 healthy women (age 25 ± 1 years). Total peripheral resistance and stroke volume were calculated. Four minutes epochs of data were analysed. Results:, Breathing rates and sympathetic activity were similar in men and women but compared to men, women had significantly lower blood pressures, cardiac output and stroke volume. In men breathing rate correlated positively with sympathetic activity (r = 0.58, P < 0.05) but not in women (r = 0.12, P > 0.05). Furthermore, in men, respiratory rate correlated positively with total peripheral resistance (r = 0.65, P < 0.05) and inversely with cardiac output (r = ,0.84, P < 0.05) and heart rate (r = ,0.60, P < 0.05) but there were no such relationships in women (P > 0.05 for all). Conclusions:, The positive relationship between breathing and sympathetic activity in men, and the inverse coupling of breathing to cardiac output and heart rate suggest that influences of respiration may be important not only for dynamic but also for ,tonic' cardiovascular function. The lack of relationships among these variables in women shows that there are fundamental differences in basic blood pressure regulation between the sexes. [source]

Arterial Rigidity And Cardiovascular Sympathetic Tone In Hypertensive Obese And Type 2 Diabetic Patients

P Valensi
An increase of arterial rigidity and sympathetic activity has been suggested to contribute to essential hypertension. We have shown that vagal control of heart rate (HR) variations during standardized tests is similarly impaired in normotensive obese and type 2 diabetic patients. The aim was to compare cardiovascular vagosympathetic balance and the link between pulse pressure, an index of arterial rigidity, and sympathetic activity in normotensive and hypertensive obese and type 2 diabetic patients. Groups 1 and 2 consisted of 70 normotensive and 32 hypertensive obese patients, groups 3 and 4 of 18 normotensive and 14 hypertensive diabetic patients respectively. HR and blood pressure (BP) variations were studied with a plethysmographic system and spectral analysis (Finapres). During a 5 min-period at a controlled breathing rate, in the 4 groups, the high frequency peak of HR variations (vagal control) was significantly lower than in controls (19 healthy subjects), and the mid/high frequency peak ratio of HR variations was significantly increased. During a standing test, the mid-frequency peak of systolic BP variations (sympathetic activity) did not differ significantly in obese or diabetic patients, either normotensive or hypertensive, and in controls. This peak correlated significantly with pulse pressure in groups 2 and 4 and in the control group but not in groups 1 and 3. In conclusion, 1) spectral analysis confirms that in obese and diabetic patients vagal control of HR variations is similarly reduced and suggests that sympathetic activity is relatively increased ; 2) in hypertensive patients sympathetic tone is not higher than in normotensive ones, but may contribute to arterial rigidity. [source]

Cardiac baroreflex control in humans during and immediately after brief exposure to simulated high altitude

Frédéric Roche
Summary To examine the baroreflex response in humans during and immediately after acute hypoxia exposure, the cardiac baroreflex sensitivity (BRS) was studied using adaptation of RR intervals in response to spontaneous systolic blood pressure fluctuations (sequences methodology) in 11 unacclimatized subjects. All measurements were made under fixed breathing rate, and realized consecutively at baseline level (20 min), at an inspired oxygen concentration of 11% (15 min) and again under normoxic conditions (20 min; recovery period). The spontaneous baroreflex response decreases progressively during hypoxic exposure, causing a tachycardic response at this FiO2 without any significant alteration of the systolic or diastolic blood pressure. The magnitude of decrease for this variable at the end of exposure averaged 42·9 ± 15·6%. The simultaneous spectral analysis of heart rate (HR) variability in hypoxic condition confirmed an alteration in the parasympathetic activity (HFnu: ,17·8 ± 30·9% versus basal conditions, P<0·01) counterbalanced by an exaggerated sympathetic activity (LFnu: +33 ± 42·4%, P<0·05) at the sinus node. Interestingly, we could observe an enhanced cardiac baroreflex response during the period following the inhalation of the hypoxic mixture (+130·6 ± 15·6% of basal conditions, P<0·001). There is a relationship with a significant and abrupt increase in the parasympathetic control of HR (mean HR reached 111 ± 8·1% of the mean basal HR, P<0·01). These results suggest that brief exposure to hypoxia under rate-controlled ventilation is associated with a significant alteration in the spontaneous cardiac baroreflex. This important cardiac autonomic imbalance is followed by a significant increase in the cardiac parasympathetic drive even after the disappearance of the hypoxic stimulus. [source]