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Pulmonary Graphics - Figure of 8


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From time to time the pressure/volume loop displays a figure of 8, when I quiz the clinicians as to what it is we are witnessing they draw a blank. The closest answer I've found is that of flow starvation, but is anyone able to break it down further for me so I can enlighten my colleagues?

Many thanks


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I assume you are referring to this:

Taken from various sources

Respiratory plethysmography During normal tidal breathing, without significant pathology, diaphragm contraction leads to inspiration followed quickly by chest wall muscle activity. However, as respiratory pathology develops, regardless of etiology, there is often an increasing amount of thoraco-abdominal asynchrony (TAA), resulting from worsening respiratory (initially intercostal) muscle fatigue. Such TAA can be measured using respiratory plethysmography. Elastic bands are placed around the rib cage (RC) and abdomen (ABD). The output of these movements is then downloaded to a computer program that displays characteristic oscillatory patterns which approximate sine waves.

The level of synchrony between these two bands, the phase angle (Θ), is then calculated: sin Θ= m/s, where m is the length of the midpoint of the RC excursion and s is the length depicting the ABD excursion. During normal breathing, the phase angle is less than 25°, and creates a very tight, counterclockwise loop . However, as TAA worsens, the loop opens and widens, with larger phase angles. Additional information is learned from the direction of rotation of the loop. If the RC leads instead of the ABD, then the loop will take on a clockwise rotation, commonly seen with bilateral diaphragm paralysis. If one hemi-diaphragm or hemi-thorax is ineffective, the loop will take on a ‘figure of 8’ appearance.

Patients with unilateral diaphragmatic dysfunction usually are more difficult to identify clinically, especially if they are infants. Although these patients may have a clinically inefficient and asynchronous breathing pattern, it may not be as obvious as in patients with bilateral dysfunction, particularly in smaller infants. As they initiate a breath with the functioning diaphragm, the contralateral diaphragm elevates. This results in a shift of the mediastinum to the unaffected side, compromising lung expansion. Graphically, this can be seen as characteristic “figure of eight” Konno–Mead loops, in which initial abdominal excursion is followed by rib cage expansion with abdominal intrusion

In the Konn0-Mead Plot we will get the initial abdominal excursion (AB) and counterclockwise loop, followed by incursion of the abdomen and a clockwise finish giving a figure of eight appearance.

Phase angle analysis on RC-AB loops is meaningless for figure-of-8 shape loops.

Cant get a simpler explanation than that ;-) !

To understand more




Edited by JACK
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Thank you JACK, simple questions and simple answers. ;-)


You are welcome ;-)

I just re-read your initial post...I think you wanted figure of 8 in V/P loops.....I totally missed that part of the question !

JACK, I will bookmark your comment!

I wonder, do one need to investigate for unilateral diaphragm paresis in a case of a 8-shaped loop?

I have seen this sometimes incidentally on x-rays (although not treated, it probably gave some explanation to need of ventilatory support)

Actually unilateral diaphragmatic paralysis is frequently faced by cardiothoracic surgeons in the post op period.....I wonder what is their approach

Do they do surgical plication for these cases?


Unilateral phrenic nerve palsy is poorly tolerated in neonates and infants in whom intercostal inspiratory mechanisms are inefficient. Clinically, the abdominal contents visibly slew to the paralysed side during spontaneous inspiration. Diaphragmatic paralysis can be confirmed by screening the diaphragm using ultrasound or video fluoroscopy or, if available, transcutaneous phrenic nerve electromyography. Although the phrenic nerve may recover slowly if it has not been divided, surgical placation of the diaphragm greatly increases efficiency of the contralateral hemi-diaphragm and usually leads to successful weaning

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