(1/1394) Factors influencing the deposition of inhaled particles.

Because the initial deposition pattern of inhaled particles of various toxic agents determines their future clearance and insult to tissue, respiratory tract deposition is important in assessing the potential toxicity of inhaled aerosols. Factors influencing the deposition of inhaled particles can be classified into three main areas: (1) the physics of aerosols, (2) the anatomy of the respiratory tract and (3) the airflow patterns in the lung airways. In the physics of aerosols, the forces acting on a particle and its physical and chemical properties, such as particle size or size distribution, density, shape, hygroscopic or hydrophobic character, and chemical reactions of the particle will affect the deposition. With respect to the anatomy of the respiratory tract, important parameters are the diameters, the lengths, and the branching angles of airway segments, which determine the deposition. Physiological factors include airflow and breathing patterns, which influence particle deposition. Various lung models used in predicting particle deposition are reviewed and discussed. The air-way structures of various animal species are compared, showing the unique structure of the human lung compared to the animal species under study. Regional deposition data in man and dog are reviewed. Recent deposition data for small rodents are presented, showing regional difference in deposition with the right apical lobe having the highest relative deposition.  (+info)

(2/1394) Particle deposition in the trachea: in vivo and in hollow casts.

The pattern of deposition within the respiratory tract of potentially harmful particulates is a major factor in assessing any risk from individual and community exposures. Although the trachea is the most easily observed of the conductive airways, very little information concerning its particle collection characteristics is available, information which is essential for a complete and realistic description of particle deposition patterns within the entire respiratory tract. Data on tracheal deposition are also needed for development of accurate predictive models for particle deposition. The pattern of particle deposition in the trachea, and its relation to air flow, was studied in a hollow cast of the human larynx-tracheobronchial tree. Results were compared with data obtained in humans in vivo and from previous studies in hollow casts. In addition, the relevance of tracheal deposition in the hollow cast test system to deposition in vivo was examined by a direct comparison of deposition in a cast prepared from the lungs of donkeys previously studied in a series of in vivo tests. The disturbance of the air flow within the trachea caused by the larynx promoted the deposition of suspended particulates throughout the length of the trachea, and especially in proximal regions. This proximal deposition was due both to direct impaction from the air jet coming from the glottis and to effects of the tubulent flow. Turbulence produced inhomogenous deposition patterns within the trachea for particles of all sizes, although its effect was more pronounced as size decreased. Tracheal deposition in the human cast was within the range of normal in vivo tracheal depostion only when a larynx was used during cast test exposures; this emphasizes the need for the use of realistic experimental test systems for the study of particle deposition patterns. The relative patterns of deposition in casts of the donkey trachea and in the same tracheas in vivo were similar.  (+info)

(3/1394) Pattern of total and regional lung function in subjects with bronchoconstriction induced by 15-me PGF2 alpha.

Closing volume (single breath nitrogen test), regional ventilation and perfusion (using intravenous xenon-133), and total lung function (TLC, VC, and FEV) were measured before and after intramuscular administration of 250 mug 15-methyl prostaglandin F2alpha (15-me PGF2alpha) in 10 healthy women. The cardiac output was measured with the Minnesota impedance cardiograph model 304A and the transthoracic impedance was used as an expression of the thoracic fluid volume. The slope of the alveolar plateau on the closing volume tracing showed a 271% increase 20 minutes after the prostaglandin administration, at which time the closing volume per cent (CV%) had decreased (P less than 0-01) and the closing capacity (CC%) had increased (P less than 0-05). Vital capacity (VC) decreased (P less than 0-01), residual volume (RV) increased (P less than 0-01), and the total lung capacity (TLC) remained unchanged. The maximal decrease (9%) in FEV1 was seen after 20 minutes. All these measurements except the slope of the alveolar plateau returned to control levels after 60 minutes. The redistribution of regional ventilation was more pronounced than that of the regional pulmonary blood flow. No change was observed in cardiac output and transthoracic impedance. None of the patients experienced any dyspnoea. Our results are consistent with a more pronounced effect of prostaglandin F2alpha on the small airways (the alveolar plateau) than on the larger airways (FEV1). In cases where an increase in the slope of the alveolar plateau is observed, the closing volume per cent should not be used as a measurement of the lung disease. It is concluded that the single breath nitrogen test (N2 closing volume) is more sensitive than the conventional tests.  (+info)

(4/1394) Effect on nasal resistance of an external nasal splint and isotonic exercise.

OBJECTIVES: The now commonplace wearing of external nasal splints by sportsmen and athletes has never been scientifically evaluated. The present study looks into the effect of isotonic exercise on nasal resistance, and examines whether this effect is altered by the wearing of an external nasal splint. METHODS: Twenty subjects not suffering from rhinitis were tested. Nasal resistance measurements were recorded using an anterior rhinomanometer before and after isotonic exercise with and without an external nasal splint. Pulse and blood pressure were measured before and after exercise. RESULTS: Significant changes were observed in pulse (p < 0.001) and both systolic (p < 0.002) and diastolic (p < 0.001) blood pressure in response to exercise. Significant differences were seen in nasal resistance when the splint was applied (p < 0.001) and after exercise (p < 0.003). No significant difference was observed after exercise when the splint was worn (p = 0.167). CONCLUSIONS: External nasal splints decrease nasal resistance at rest but are of little value during isotonic exercise.  (+info)

(5/1394) Cardiopulmonary responses of middle-aged men without cardiopulmonary disease to steady-rate positive and negative work performed on a cycle ergometer.

BACKGROUND AND PURPOSE: Understanding physiological responses to negative work allows therapists to be more knowledgeable when they prescribe this form of exercise. The physiological responses of 12 men without cardiopulmonary disease, aged 39 to 65 years (X=49.7, SD=9.3), to negative work (eccentric muscle contractions) and to positive work (concentric muscle contractions) were compared. SUBJECTS AND METHODS: Subjects performed the 2 types of work on a motorized cycle ergometer at pedaling frequencies of 35, 55, and 75 rpm with a constant power output of 60 W. Steady-rate values of oxygen consumption (VO2), heart rate (HR), minute ventilation (VE), tidal volume (VT), and breathing frequency (fb) were obtained during 6 test conditions (positive and negative work at each of the 3 pedaling frequencies). RESULTS: Values for all measures were greater during positive work than during negative work, except for fb. During positive work, values for all variables were greatest at 75 rpm, except for fb. During negative work, VO2 and HR were greater at 75 and 35 rpm than at 55 rpm, and VE and VT were greater at 75 rpm than at 55 rpm. Breathing frequency was not different among pedaling frequencies. CONCLUSION AND DISCUSSION: The results confirmed that negative work performed on a cycle ergometer is associated with low metabolic cost in older men without cardiopulmonary disease. Although VE was determined primarily by changes in VT during negative work, a comparable disproportionate increase in fb was observed at the start of negative work. Such changes in breathing patterns have implications for the prescription of negative work for patients with lung disease.  (+info)

(6/1394) Contribution of gular pumping to lung ventilation in monitor lizards.

A controversial hypothesis has proposed that lizards are subject to a speed-dependent axial constraint that prevents effective lung ventilation during moderate- and high-speed locomotion. This hypothesis has been challenged by results demonstrating that monitor lizards (genus Varanus) experience no axial constraint. Evidence presented here shows that, during locomotion, varanids use a positive pressure gular pump to assist lung ventilation. Disabling the gular pump reveals that the axial constraint is present in varanids but it is masked by gular pumping under normal conditions. These findings support the prediction that the axial constraint may be found in other tetrapods that breathe by costal aspiration and locomote with a lateral undulatory gait.  (+info)

(7/1394) Influence of immersion on respiratory requirements during 30-min cycling exercise.

Immersion is considered to facilitate exercise-based rehabilitation. However, the drag effect of moving limbs in water, likely to increase the respiratory requirements at exercise, is not mentioned in many reports. The energetic and ventilatory requirements of 30 min steady state cycling exercise performed by healthy male subjects in air and during immersion up to the xiphoid in 33 degrees C water were compared. In the first experimental series nine subjects exercised at the same 60% maximal oxygen consumption (V'O2,max) in air and water. In the two ambient conditions, ventilatory variables had similar values, but the ergometric setting had to be reduced during water immersion so that the workload rated only 69+/-20 W (mean+/-SD) in water versus 121+/-32 W (p<0.001) in air. In the second experimental series, the same ergometric work load (122 W) was achieved by nine subjects with an average V'O2 of 2,210+/-300 mL x min(-1) in air versus 2,868+/-268 mL x min(-1) in water (p<0.001). Resting water immersion caused a marked trend for decreasing vital capacity (p=0.06), but no modification of other ventilatory variables. During exercise at similar V'O2, the average values of minute ventilation (V'E), tidal volume (VT), respiratory frequency (fR), tidal inspiratory time (VT/tI) were not different between water and air. However, at similar ergometric workload, V'E, VT, fR, VT/tI and plasma lactate levels were significantly higher in water than in air. Such consequences of the drag effect of water upon limb movements have not been reported in previous studies relying on shorter exercise bouts. Thus, maintaining steady exercise levels in water either led to a decrease in the workload or required a 25% higher oxygen consumption than in air. These findings may be relevant to the prescription of water immersion rehabilitation programmes.  (+info)

(8/1394) Effects of chemical feedback on respiratory motor and ventilatory output during different modes of assisted mechanical ventilation.

The purpose of the study was to examine the effects of chemical feedback on respiratory motor and ventilatory output in conscious subjects ventilated on various modes of assisted mechanical ventilation. Seven subjects were connected to a ventilator and randomly ventilated on assist-volume control (AVC), pressure support (PS) or proportional assist ventilation (PAV). On each mode, the assist level was set to the highest comfortable level. Airway and oesophageal (Poes) pressures, tidal volume, respiratory frequency (fR) and end-tidal carbon dioxide tension (PET,CO2) were measured breath-by-breath. When the subjects were stable on each mode, the fraction of inspired carbon dioxide (FI,CO2) was increased stepwise, and changes in minute ventilation (V'E) and respiratory motor output, estimated by the pressure-time product of all the respiratory muscles per breath (PTPrm) and per minute (PTPminute), were observed. At zero FI,CO2, PTPminute/PET,CO2 did not differ between modes, while V'E/ PTPminute was significantly lower with PAV than that with PS and AVC. As a result V'E/PET,CO2 was significantly lower with PAV, preventing, unlike AVC and PS, a significant drop in PET,CO2. With PAV, independent of CO2, V'E/PTPminute remained constant, while it decreased significantly with increasing CO2 stimulus with PS and AVC. At high PET,CO2 respiratory effort was significantly lower with PAV than that with PS and AVC. In conclusion, the mode of mechanical ventilation modifies the effects of chemical feedback on respiratory motor and ventilatory output. At all carbon dioxide stimulus levels neuroventilatory coupling was better preserved with proportional assist ventilation than with pressure support and assist-volume control ventilation.  (+info)