Pulmonary Artery Pressure

Operation gives baby Ashtyn Thomas new life

Nine-month-old Ashtyn Thomas has a rare condition called pulmonary artery sling. Normally the artery, which comes out of the right side of the heart and pumps blood through the lungs, is not near the airways.

But in Ashtyn's case, one branch was between the windpipe (trachea) and the foodpipe (oesophagus), putting pressure on the windpipe. In addition, the cartilage rings around her air pipe were circular instead of horseshoe shaped.

This meant her trachea was being squeezed so tight it was hard to breathe.

Chief of paediatric medicine Professor Colin Robertson said her windpipe was so constricted that in one section it was just 1mm wide, instead of 6mm.

Parents Belinda Lomman and James Thomas, from Jamestown about 200km north of Adelaide, said Ashtyn had difficulty feeding from birth.

"She was also wheezing and finding it hard to breathe," Mr Thomas said.

About 12 weeks ago, she stopped feeding and her weight plummeted.

Doctors diagnosed her with bronchiolitis, a common respiratory infection, but she did not respond to antibiotics. Finally, last month, her lung collapsed and she was taken to intensive care.

"She looked at me and ...you could see she was so scared she couldn't breathe," Ms Lomman said.

A CT scan revealed the constricted windpipe.

Ashtyn was flown to Melbourne with the Royal Flying Doctor Service. She had an operation to cut out the strangled section of windpipe and reattach the normal sections.

"If we hadn't fixed her airways she would have died," Prof Robertson said. "It's normally really tricky surgery so in the old days most of these children would die."

Ashtyn is expected to make a full recovery.

vandenbergL@heraldsun.com.

Pulmonary Heart Disease

The heart and the respiratory system are closely connected such that disorders of one system influence the function of the other. In the 1800s, Laennec described patients with pulmonary emphysema and associated right heart enlargement. In the 1930s, Paul Dudley White recognized that, although left heart disease is the most common cause of right ventricular enlargement and dysfunction, enlargement of the right ventricle (RV) can result from lung disease in the absence of left heart failure. He coined the term cor pulmonale to describe this condition, also known as pulmonary heart disease (PHD). With the advent of technological advances in cardiovascular physiology and diagnosis, there has been an impressive advance in our knowledge of the manner in which disordered respiratory function affects the heart, especially the RV. Uniformly accepted criteria for defining PHD do not exist; hence, precise estimates of its prevalence are difficult to ascertain. However, heart failure on the basis of PHD probably constitutes at least 15% to 20% of all cases of heart failure and 7% to 10% of all heart disease. Some 40% of patients with severe chronic obstructive pulmonary disease demonstrate clinical or pathologic evidence of PHD. This is especially important because PHD implies a grave prognosis. Only approximately one-third of patients with lung disease and PHD will be alive 4 years after diagnosis, as opposed to 64% of those without PHD. Pulmonary heart disease is heart disease caused by dysfunction of the lungs leading to altered pulmonary vasculature. McGinn and White used the term acute cor pulmonale to describe right heart strain resulting from acute pulmonary hypertension. This is in contrast to chronic cor pulmonale, which has been defined by the World Health Organization as an alteration in structure or function of the RV resulting from disease affecting the structures and function of the lung except when this alteration results from disease of the left heart or congenital heart disease. This definition, based on alterations in structure, has been challenged in favor of more functional definitions containing elements of clinical syndromes, i.e., right heart failure. However, these definitions are similarly imprecise, and there seems no reason to depart from the classic definition. Thus, PHD may be associated with varying degrees of clinically apparent heart failure or abnormalities in pulmonary hemodynamics or may, in many cases, be clinically silent. In this chapter, we review some of the factors that characterize acute and chronic PHD. Because PHD is a disease of the RV, we briefly describe normal RV function and the response of the RV to imposed mechanical loads. We consider the interactions between the RV and the LV because these are so important to the normal functioning of the heart. We then consider the clinical and pathophysiological features of acute and chronic PHD. Details of pulmonary circulation and pulmonary hypertension have been reviewed in previous chapters. The RV develops embryologically from two separate components of the primitive cardiac tube. The bulbus cordis is incorporated into the conus (outflow tract), and the sinus venosus is incorporated into the sinus (inflow tract). Normal RV contraction preserves the functional distinction of its dual embryologic origin. Right ventricular systole occurs by sequential contraction, beginning at the inflow tract and extending to the outflow tract, and is almost peristaltic in nature, with approximately 25 msec separating contractile activity of the two components. In fact, with increased sympathoadrenal activation, a pressure gradient can develop between the inflow and outflow tract within the ventricular cavity. This mode of contraction makes the RV ideally suited for its job as a high-volume low-pressure pump. The RV is normally thin (less than 0.5 cm thick) and crescent shaped. Therefore, determination of its volume from limited numbers of dimensions that can be assessed using standard imaging techniques is more difficult than for the left ventricle (LV). The difficulty in measuring RV volume using simple imaging techniques (as for the LV) is further compounded by the fact that, with dilation, its shape becomes more ellipsoidal. Thus, changes in loading conditions can lead to changes in shape. This in turn may be responsible for the fact that in many circumstances there is a poor or nonexistent correlation between end-diastolic and end-systolic pressures and corresponding RV volumes. The fact that the RV free wall may be ablated or surgically replaced with a dacron patch with no change in resting cardiac output initially led workers to believe its importance to circulatory homeostasis is minimal. However, when there is an increase in pulmonary arterial pressure or venous return, as with exercise or other stress, normal RV functioning is essential for maintenance of normal circulatory status. It is commonly stated that the RV is a “volume pump,” whereas the LV is a “pressure pump,” implying some sort of qualitative difference between the ventricles. It is certainly true that the thin-walled RV is less able to generate pressure than the muscular LV (Table 1). However, compared to its normal physiological pressure range, the RV is capable of increasing maximum pressure generation proportionally to the same degree or even more than the LV. During acute constriction of the pulmonary artery, maximum RV pressure can increase to 55 to 60 torr (almost three times the normal peak systolic pressure) before circulatory failure ensues.

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