Respiratory response to acute progressive pneumothorax

Function of the canine inspiratory muscle pump in pleural effusion: influence of body position

Pleural effusion, a complicating feature of many diseases of the lung and pleura, adversely affects the pressure-generating capacity of the diaphragm in supine dogs. The objective of the present study was to assess the impact of body position on this effect and to evaluate the adaptation to effusion of the inspiratory muscle pump during breathing. Two experiments were performed. In the first, progressively increasing effusion was induced in anesthetized animals, and the changes in pleural (ΔPpl) and abdominal (ΔPab) pressure were measured during isolated phrenic nerve stimulation while the animals were placed in both the supine and the 45° head-up posture. In the second experiment, graded pleural effusion was also performed, and ΔPpl, ΔPab, and the electromyogram of the parasternal intercostal muscles were measured while the vagotomized animals were breathing spontaneously in the same two postures. The data showed that with effusion 1) ΔPpl during phrenic nerve stimulation was substantially lower with the animals in the head-up than in the supine posture; 2) this postural effect was primarily the result of the decrease in muscle length in the head-up posture; 3) during spontaneous breathing, however, parasternal intercostal inspiratory activity increased and ΔPpl remained unaltered while ΔPab decreased; and 4) the decrease in ΔPab and in the ΔPab/ΔPpl ratio was much larger in the head-up than in the supine posture. It is concluded that in the presence of pleural effusion, the pressure contribution of the inspiratory intercostal muscles during breathing increases and compensates for the shortening of the diaphragm, particularly in the upright posture.

Pneumothorax: A Review

Pneumothorax is a pathological condition in which air accumulates within the thoracic cavity. Pneumothorax affects animals without sex or age predilections; however, it has been suggested that the Siberian husky breed of dog has a predisposition for spontaneous pneumothorax. Pneumothorax occurs as the result of trauma or underlying disease and can present a clinical challenge with regard to diagnostic and therapeutic techniques. Topics reviewed include normal lung physiology; the pathogenesis, diagnosis, treatment, complications, and prognosis of pneumothorax; and current techniques in animals and humans.

Pneumothorax

This article reviews the classification, etiopathogenesis, and treatment for the various forms of pneumothorax. Traumatic and nontraumatic pneumothoraces are discussed. New theories on the etiology and treatment of primary spontaneous and secondary pneumothorax are mentioned.

Thoracic trauma

The physiologic equilibrium of chest injury patients is frequently precarious, and mild stress during examination and treatment may precipitate acute decompensation and death. This is particularly true with the respiratory system, where the normally large respiratory reserve capacity may be rapidly lost. Accurate assessment of the nature of the thoracic injury and the severity of that injury must be determined in order to formulate a therapeutic plan. Many thoracic injuries, such as pneumothorax, pulmonary contusions, or rib fractures, will be self-limiting. Other conditions must be recognized for their potentially lethal nature and dealt with aggressively, and these include cardiac tamponade, tension pneumothorax, and esophageal perforation. By performing a systematic evaluation of the patient and confirming or denying the presence of all possible types of thoracic injury, the veterinarian may avoid overtreatment of self-limiting lesions and recognize and aggressively treat those with potentially fatal outcomes.

Studies on laryngeal calibre during stimulation of peripheral and central chemoreceptors, pneumothorax and increased respiratory loads

1. The effects of asphyxia, hypoxia, hypercapnia, stimulation of peripheral chemoreceptors, pneumothorax and breathing through resistances have been investigated on laryngeal resistance to airflow in anaesthetized cats, with and without bilateral vagotomy below the origin of the recurrent laryngeal nerves.2. Resistance to airflow of the innervated larynx was usually measured with the larynx isolated in situ with constant flow from the trachea to a pharyngeal opening, and expressed by the relationship between translaryngeal pressure and airflow.3. Asphyxia, hypoxia and hypercapnia each stimulated breathing and decreased laryngeal resistance to airflow, in both the inspiratory and expiratory phases. After vagotomy the effect was reduced, abolished or (usually) reversed to a laryngeal constriction, especially in expiration.4. Intra-arterial injections of potassium cyanide (to stimulate carotid body chemoreceptors) caused a short apnoea or an augmented breath followed by hyperpnoea, concurrently with expiratory constrictions of the larynx. The responses were usually stronger after bilateral vagotomy.5. Pneumothorax caused tachypnoea, inspiratory dilatations and expiratory constrictions of the larynx. The responses were abolished by vagotomy.6. Imposition of respiratory resistances dilated the larynx, in inspiration and expiration, while complete closure of trachea caused expiratory constrictions of the larynx. These changes did not depend on intact vagal pathways.7. The results are discussed in terms of nervous control of the larynx in the different conditions.

The activity of lung irritant receptors during pneumothorax, hyperpnoea and pulmonary vascular congestion

1. The activity of lung irritant receptors during pneumothorax, hyperpnoea and pulmonary congestion has been studied by recording from single vagal nerve fibres from the receptors in rabbits.2. The receptors were stimulated during induction and during removal of pneumothorax.3. Pneumothorax caused a greater depression of minute volume in bilaterally vagotomized rabbits, compared with those with intact vagus nerves.4. Hyperpnoea due to breathing through an added dead space increased the discharge of the receptors. Experiments on paralysed and artificially ventilated rabbits showed that this was not a direct action of the asphyxial changes in blood gas tensions.5. Pulmonary congestion, induced by inflating a balloon in the left atrium, stimulated the receptors in paralysed artificially ventilated rabbits.6. The evidence that the receptors cause vagal reflex hyperpnoea and bronchoconstriction is discussed, together with their role in the reflex ventilatory and bronchomotor changes in the conditions studied.