Ventilatory rate

Subjected to steadily increasing concentrations of waterborne cyanide over a 9-h period 200 at 1 h, 600 at 3 h, 1000 at 5 h, and 1800 at 9 h Increased heart beat rate at lowerconcentrations and decreased rate at higher concentrations hyperventilation in first 3 h, followed by decrease in ventilation rate oxygen consumption paralleled changes in heart and ventilatory rates death in 9 h 21... 

Industrial processes, such as mUling and mining, construction work, and the burning of wood or fossil fuel, generate particulates that can be directly toxic or can serve as vectors for the transfer of bound material, such as sulfuric acid, metals, and hydrocarbons, into the lungs. Natural products such as pollen, anthrax spores, and animal dander can elicit toxic reactions on inhalation or skin contact. The inhalation of asbestos, silica, or coal dust can cause pneumoconiosis, which may develop into serious lung disease. The size of the particle, ventilatory rate, and depth of breathing will determine the extent of pulmonary deposition. 

Alveolar wash-in This term refers to the replacement of the normal lung gases with the inspired anesthetic mixture. The time required for this process is directly proportional to the functional residual capacity of the lung, and inversely proportional to the ventilatory rate it is independent of the physical properties of the gas. Once the partial pressure builds within the lung, anesthetic uptake from the lung begins. 

Egle (1972) exposed anesthetized dogs to concentrations of acrolein between 172 and 262 ppm for a brief period of time (1-3 minutes) and observed that acrolein uptake by the total respiratory tract at ventilatory rates of 6-20 respirations/minute averaged 80-85% of the inhaled dose. Retention was independent of the respiratory rate. The author estimated that only about 20% of the inhaled dose reached the lower respiratory tract. Exposure of the lower respiratory tract alone resulted in 65-70% concentration-independent retention, but decreased slightly with increases in tidal volume from 100 to 160 mL. Although the study by Egle (1972) does not provide information on the disposition of the retained acrolein or on whether the uptake rates represent steady-state values, it indicates that... 

The aqueous extracts of Crinum glaucum caused an increase in tidal volume, increase in ventilatory rate and depth (115). The extract also inhibited the quantity of mediators antigenically released from the limgs, inhibited mast cell degranulation and reduced the mepyramine resistant activity from the limgs. These effects substantiate the efficacy of the extract in the treatment of asthma (116, 117). Aqueous and ethanohc extracts of Crinum zeylanicum have shown high mortality rate of the molluscides Biomphalaria pfeifferi and Lymnaea natalensis (118). 

PSV is a type of mechanical ventilation that uses a patient s inspiratory effort and supplements to a select level of positive airway pressme. The patient controls the ventilatory rate and inspiratory assist time, whereas the PSV supplements inspiratory flow and tidal volume. Because PSV is heavily reliant on the patient s effort, this form of ventilation may not be optimal in patients unable to generate sufficient effort. However, it is the modality of choice in patients who are unable to synchronize with other modes of support. 

The symptoms of overdosage are usually somnolent but may be stuporous or comatose and convulsing. Respiratory depression is characteristic the ventilatory rate or tidal volume is decreased, resulting in cyanosis and hypoxia. Pupils, initially pinpoint, may dilate as hypoxia increases. Cheyne-Stokes respiration and apnea may occur. BP falls, and cardiac performance deteriorates, resulting in pulmonary edema and circulatory collapse, unless corrected promptly. Cardiac arrhythmias and conduction delay may be present. 

Metabolic acidosis can result in stimulation of chemoreceptors, leading to increased ventilatory rate and depth and Kussmaul breathing in an attempt to decrease CO to compensate for the excess acid in the body. If the hyperventilation is prolonged, fatigue could result, leading to respiratory failure. 

Uptake Kinetics. Determination of the rate of uptake can provide very useful information about bioaccumulation. In dynamic environments, where conditions are changing and water-sediment equilibrium is not achieved, a compound that is slowly taken up may allow the animal to avoid harm as it moves between high and low exposure concentrations. The rate of uptake is also of interest under spill conditions where a substance such as oil is released into the environment and achieves high concentrations for a short time. Althdugh it is well known that fish and crustaceans can metabolize PAHs much more efficiently than clams or polychaetes, and hence possess faster elimination rates, it is also apparent that crustaceans and fish have very rapid rates of uptake (Neff et al. 1976), which may be related in part to high ventilatory rates. 

When cyanosis occurs, oxygen should be supplemented by a facemask or by an oropharyngeal airway with a flow rate of about 7 liters/min. When indicated or when there is a ventilatory insufficiency, intubation should be performed to support breathing. Patients who are vomiting should be positioned adequately in order to avoid aspiration (table 1). 

Beyond this point, during more severe exercise associated with anaerobic metabolism, minute ventilation increases faster than the rate of oxygen consumption, but proportionally to the increase in carbon dioxide production. The mechanism of the ventilatory response to severe exercise involves metabolic acidosis caused by anaerobic metabolism. The lactic acid produced under these conditions liberates an H+ ion that effectively stimulates the peripheral chemoreceptors to increase ventilation. 

Some patients lose the ability to increase the rate or depth or respiration in response to persistent hypoxemia. This decreased ventilatory drive may be due to abnormal peripheral or central respiratory receptor responses. This relative hypoventilation leads to hypercapnia in this situation the central respiratory response to a chronically increased PaC02 can be blunted. Because these changes in Pa02 and PaC02 are subtle and progress over many years, the pH is usually near normal because the kidneys compensate by retaining bicarbonate. 

Noninvasive positive-pressure ventilation (NPPV) provides ventilatory support with oxygen and pressurized airflow using a face or nasal mask with a tight seal but without endotracheal intubation. In patients with acute respiratory failure due to COPD exacerbations, NPPV was associated with lower mortality, lower intubation rates, shorter hospital stays, and greater improvements in serum pH in 1 hour compared with usual care. Use of NPPV reduces the complications that often arise with invasive mechanical ventilation. NPPV is not appropriate for patients with altered mental status, severe acidosis, respiratory arrest, or cardiovascular instability. 

Modeling of gas transport is also useful for correlating dose-response data obtained under different conditions. Brain suggested that the total dose of an inhaled gas is relate to ventilation rate, duration of exposure, and gas concentration before inhalation. Folinsbee et al. exposed human subjects to ozone at 0.37, 0.5, or 0.75 ppm for 2 h while they were at rest or exerdsing intermittently. The primary response of the subjects was an alteration in the exercise ventilatory pattern. They... 

In human subjects, concentrations of about 5mg/m were objectionable, usually causing cough, with an increase in respiratory rate and impairment of ventilatory capacity. ... 

Vallebona A, Gigli G, Orlandi S, Reggiardo G. Heart rate response to graded exercise correlates with aerobic and ventilatory capacity in patients with heart failure. Clin. Cardiol. 2005 28 25-9. 

Nitrous oxide decreases tidal volume and increases the rate of breathing and minute ventilation. Although arterial carbon dioxide partial pressures tend not to be affected the normal ventilatory responses to carbon dioxide and to hypoxia are depressed. Alveolar collapse in structured lung segments may be more rapid in the presence of nitrous oxide than with oxygen due to its greater solubility. Similarly, it depresses mucous flow and chemotaxis. In theory these factors predispose to postoperative respiratoiy complications. 

With the exception of nitrous oxide, all inhaled anesthetics in current use cause a dose-dependent decrease in tidal volume and an increase in respiratory rate. However, the increase in respiratory rate is insufficient to compensate for the decrease in volume, resulting in a decrease in minute ventilation. All volatile anesthetics are respiratory depressants, as indicated by a reduced response to increased levels of carbon dioxide. The degree of ventilatory depression varies among the volatile agents, with isoflurane and enflurane being the most depressant. All volatile anesthetics in current use increase the resting level of Paco2 (the partial pressure of carbon dioxide in arterial blood). 

---