Hamman Rich syndrome (fibrosing alveolitis) and so on Aiveolar hypove ntiIation in This condition.

gory of non-revarsble defect, emphysema is a tipical example in advanced emphysema the negativity of intrapleurral pressure tends to disappear to that traction on the bronchial tubes becomes less than normal This produces a tendency of that Bronchial tree to collapse particularly during expiration (b) Non-Obstructive ventilator, defects restrictive generalized fibrosis of the lungs atypical example, Because of the fibrosis, the lungs do not expand statisfactonly resulting in ventilator defects Hypodynemic Disease of the thoracic wall leading to stiffness of the thoracic wall. Paralysis of the muscles of inspiration lading to weak respiratory movement is good example of this group. Defective gaze out exchange The term alveocapilary block' means a condition where due to ( thickness of the alyeolocapillary barrier the gaseous exchange 11 defective Eumple pulmonary edema, pneumonia. Hamman Rich syndrome (fibrosing alveolitis) and so on Aiveolar hypove ntiIation in This condition. respirtory are reducally due to (fault in the re spirator y center Examples of this type are drug inductd hypofunction of the respiratory center (morphine/ barbiturate), and lesion in the stem Pickwickian syndrome also falts in this category. The extremely rare and fascinating syndrome called Ondine's curse also comes in this category. Alveolar hypoventilation may also be due to hypody namic ventilatory defects like diaphragmatic paralysis: SPlROMETER In this instrument (fig.4.6.3a) a lid, 1. rests over water contained in a container, C. Arrangements ara such that when the subject breathes. he breathes in and out through a tube connected with the spirometer, and when he expires. the lid 1 is pushed up and when he inspires the lid 1. goes down. The movements of the lid (which are up wards and' down wards) are recorded on a graph paper. The graph paper is pasted over a drum and the drum is movad by a motor. The speed of the drum can be regulated and the reconding arrangement is such that when an inspiration is taken, it results in an upward stroke on the graph paper and expiration cause downward stroke. The graph paper is calibhrated so that the investigator can know the volume of air (in ml) equivalent to 1 mm of movement in the upward or downward direction (e.g. 1 mm = 30 ml of air). Similarly the speed of the drum being known the abscissa represents time in seconds. Lung volumes and lung capacities (fig. 4. 6. 4) Tidal volume (VT) is the volume of air inspired or ex-pired b an individual peres irato excursion at rest:. value for normal healthy young adult is about 500 ml. Inspiratory Reserve Volume. From top end of a tidal volume (VT) inspiration phase. the subject makes a maximal inspirtory effort. The extra air that is drawn in (fig 4 .6. 4) is the inspiratory reserve volume (IRV) Normal value is about 2000 to 3000 ml. Expiratrory reserve volume (ERV) From the end expiratory position (fig. 4.6.4) of the tidal volume breathing, the subject makes the hirdest eipiratory effort The exrtra air that comes out isThe EPV Normal value is about 1000 ml. Residual Volume (RV)after even the severest expiratory effort the lungs. sill contain some air. called residual volume. Normal value, about 1500 ml Capacities: Inspiratory capacity (IC) = IRV +VT Functional residual capacity (FRC) = ERV + RV (i) Vital Capacrly = Inspiratory capacity +ERV Note that as a rule, a 'capacity' includes more than one volume Vital capacity (VC. also called forced -vital capacity. FVC) By definition. it is the volume of air breathed out by the most forcible expiratory elrort after a maximal inspiration. As stated eartier VC or FVC = IC + ERV Therefore. in normal persons, its value should be about (2500 to 3500 ml) + 1000 ml, that is between 3. 5 to 4.5 liters, approximately VC depends on many factors, some are given below Age VC is low in old people Size Normally. VC rt about 2. 6 1/sq meter of body surface in male and 2.1 1/sq meter in females. Posture: In lying position it is low. it is highest when the subject is seated in slightly reclined position in a Chair Posture affects the VC because the position of diaphragm and the tone of abdominal muscles change with posture. On lying the diaphragm goes little up whereas on standing. the abdominalc mustles become tense, both reducing the VC Sex As noted already. VC is lower in the females Physical training A well trained stponsman or a hardworkmg manual labourer has a higher VC Following well known condition Cen reduce the VC A Physiological in pregnancy, (pertculariy in advanced stage) VC n low This u due to the inablity of the diaphfagm to go down satisfactonly B PathalogicalDneases of the lungs (emphysema. fibrosn), pleura (pleural effusion), heart (congestive cardiac failure), chest wall (kyphcsis). abdominal cavity (ascites) are common diseases known for their ability t0 reduce VC Utility of the VC measurement VC is often of prognostic value (ii) it gives also an idea about the progress of a chronic disease Thus, in a case of emphysema, gross, reduction of VC isof unfavourable prognosis Or, in the same case of emphysema, over a few years, if the VC shows prgressive detenoration, the physician understands that the taease is steadily progressing (iii) In assessment of physical fitness. VC is of some help Thus in highly physically fit perrsons (sportsmen) VC is high, and vice versa Timed vital capaciy In early stages of many chronic diseases, e. o emphysema. the volume of VC may remain withim normal limits but the Timed vital capacity may show