Tidal volume

TABLE 5.6 Effect of Dead Space Volume, Tidal Volume, and Breathing Frequency on Alveolar >fentllation at a Fixed Minute Ventilation (V = 58.0 Umin). Modified from Chemiack. ... 

Tidal volume (V ) Volume of air inspired or expired with each breath. 

Tidal volume The volume of gas inhaled or exhaled during each cycle of breathing. 

Vl = volume ot lung compartment based on tidal volume, t- a t-... 

It is imperative to identify serious causes of respiratory alkalosis and institute effective treatment. In spontaneously breathing patients, respiratory alkalosis is typically only mild or moderate in severity and no specific therapy is indicated. Severe alkalosis generally represents respiratory acidosis imposed on metabolic alkalosis and may improve with sedation. Patients receiving mechanical ventilation are treated with reduced minute ventilation achieved by decreasing the respiratory rate and/or tidal volume. If the alkalosis persists in the ventilated patient, high-level sedation or paralysis is effective. 

Most lung deposition models are based on the influence of particle size on aerosol deposition. Breathing parameters, such as breathing frequency and tidal volume, play a key role in lung deposition [15]. Table 2 shows the breathing parameters for healthy male volunteers subjected to various levels of exercise on a bicycle ergometer [16], There are known differences in these parameters based on gender, age, and disease... 

Define tidal volume, residual volume, expiratory reserve volume, and inspiratory reserve volume... 

Total ventilation. The total ventilation (minute volume) is the volume of air that enters the lungs per minute. It is determined by tidal volume and breathing frequency ... 

Total ventilation = tidal volume x breathing frequency = 500 ml/breath x 12 breaths/min = 6000 ml /min... 

With an average tidal volume of 500 ml/breath and breathing frequency of 12 breaths/min, 6000 ml or 61 of air move in and out of the lungs per minute. These values apply to conditions of normal, quiet breathing tidal volume and breathing frequency increase substantially during exercise. 

Alveolar ventilation. Alveolar ventilation is less than the total ventilation because the last portion of each tidal volume remains in the conducting airways therefore, that air does not participate in gas exchange. As mentioned at the beginning of the chapter, the volume of the conducting airways is referred to as anatomical dead space. The calculation of alveolar ventilation includes the tidal volume adjusted for anatomical dead space and includes only air that actually reaches the respiratory zone ... 

Frequency of action potential generation and duration of this electrical activity to the motor neurons, and therefore the muscles of inspiration and expiration, which determines the depth of breathing, or the tidal volume (as the frequency and duration of stimulation increase, the tidal volume increases)... 

Pulmonary stretch receptors are responsible for initiating the Hering-Breuer reflex. These stretch receptors are located within the smooth muscle of large and small airways. They are stimulated when the tidal volume exceeds 1 1. Nerve impulses are transmitted by the vagus nerve to the medullary respiratory center and inhibit the inspiratory neurons. The primary function of these receptors and the Hering-Breuer reflex is to prevent overinflation of the lungs. 

During exercise, the increase in minute ventilation results from increases in tidal volume and breathing frequency. Initially, the increase in tidal volume is greater than the increase in breathing frequency. As discussed earlier in this chapter, increases in tidal volume increase alveolar ventilation more effectively. Subsequently, however, as metabolic acidosis develops, the increase in breathing frequency predominates. 

Fig. 1. Deposition of inhaled particles of different sizes (mass median aerodynamic diameters) in the three regions of the respiratory tract. Each shaded area indicates the variability of deposition when the aerosol distribution parameter, o, (geometric standard deviation) was varied from 1.2 to 4.5. The assumed tidal volume was 1450 cm3. (Reproduced from Health Physics, vol. 12, pp. 173-207,1966 by permission of the Health Physics Society).

Unless otherwise indicated, exposure hazards are for a "standard" man (i.e., a male weighing 70 kg/154 lbs) with a respiratory tidal volume of 15 L/min (i.e., involved in light activity). If a different breathing rate is used, then it is indicated in parentheses. If temperature is a factor, then the critical values are indicated. The military typically classifies moderate temperatures as 65-85°F. Temperatures above 85°F are classified as hot. For any given parameters, a dash (i.e., —) means that the value is unavailable because it has not been determined or has not been published. 

Physical symptoms include dizziness, dysarthria, ataxia, nystagmus, lid ptosis, tachycardia, sweating, and increased deep tendon reflexes. Most subjects show some degree of hypertension, associated with increased minute and tidal volumes of respiration, increased formation of urine, and increased muscle tone. The latter may lead to increased serum creatinine phosphokinase concentration. With very large doses, convulsions and respiratory arrest are the terminal events (11). The course of clinical symptoms and signs following various doses of PCP is shown in Table 2. 

Six male Wistar rats inhaled HCN at 55 ppm for 30 min (Bhattacharya et al. 1984). HCN was generated by reaction of KCN with sulfuric acid and circulated through the chamber at the rate of 1 L/min. The rats were fitted with a lung mechanics analyzer (Buxco Electronic Inc.), and changes in air flow, transthoracic pressure, tidal volume, compliance, resistance, respiratory rate, and minute volume were determined every 10 min. Animals were sacrificed immediately following the exposure, and lungs were excised and analyzed for phospholipids (surfactant). 

An average man inhales approximately 7.5, 28.6, and 42.9 liters of air per minute during resting, light work, and heavy work periods, respectively, and the corresponding mean tidal volumes of 750, 1673 and 2030 ml (National Academy of Sciences, 1958). Each breath is distributed between 300-400 million alveoli, where gas exchange takes place. The total alveoli surface area is approximately 75m2, which is penetrated by approximately 200 km of capillary blood vessels (Hatch... 

In general, slow, deep inhalation followed by a period of breath holding increases the deposition of aerosols in the peripheral parts of the lungs, whereas rapid inhalation increases the deposition in the oropharynx and in the large central airways. Thus, the frequency of respiration (the flow velocity) and the depth of breath (tidal volume) influence the pattern of pulmonary penetration and deposition of inhaled aerosols. Therefore, an aerosol of ideal size will penetrate deeply into the respiratory tract and the lungs only when the aerosols are inhaled in the correct manner (Sackner, 1978 and Sackner et al., 1975). 

By simultaneous monitoring of tidal volume and respiratory rate, or minute volume, and the concentration of an inhaled vapor in the bloodstream and the vapor in the exposure atmosphere, pharmacokinetic studies on the C t relationship have shown that the effective dose was nearly proportional to the exposure concentration for vapors such as 1,1,1-trichloroethane (Dallas et al., 1986), which has a saturable metabolism, found that the steady-state plasma concentrations were disproportion-ally greater at higher exposure concentrations. 

Respiratory System. Tidal volume, bronchial resistance, compliance, pulmonary arterial pressure, blood gases. 

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