Measurement of Lung Volumes

More detailed assessment of lung function usually involves the measurement of the static lung volumes. These can be very helpful in sorting out restrictive and obstructive disorders. The most important measurements are total lung capacity (TLC), residual volume (RV) and functional residual capacity (FRC) which is the gas volume remaining in the lungs after the vital capacity (VC) has been exhaled. We are able to measure absolute lung volumes beyond the inspired and expired volumes measured by spirometry.

Several methods can accomplish this. Each method has its own advantages and disadvantages. The two dilutional lung volume methods, helium (He) dilution and nitrogen (N2) washout involve having the patient breathe gases or gas concentrations not normally present in the lungs whilst the third method uses the body plethysmograph to measure the volume of thoracic gas (VTG).

We are fortunate in our lab to have the “Gold-standard” measurement VMAX body plethysmograph which delivers precision engineering of the highest quality.

The body plethysmograph is a pulmonary function system consisting of a panorama glazed cabinet in which the patient sits during the test and a computer that controls testing and data output.

Our body box’s ease of operation, patient comfort and reliability will meet pulmonary function testing needs for years to come. The streamlined testing allows the scientist to focus on the patient.

FRC measured with the body plethysmograph (FRCpleth) refers to the volume of intrathorax gas measured when airflow occlusion occurs at FRC. The technique is based on Boyle’s law relating pressure to volume. Boyle’s law states that volume varies inversely with pressure if temperature is held constant. Measurement of FRCpleth is a complex procedure achieved by carefully instructing each patient in the required manoeuvres.

Plethysmography offers several advantages over other methods of measuring lung volumes.

1. VTG is not affected by the distribution of ventilation
2. Multiple measurements can be made quickly and averaged
3. and it provides a more accurate estimate of lung volumes in patients who have airway obstruction.

In general, the body box is regarded as the more acceptable technique, but is more demanding for the patient and more technically complex.

It is often useful to compare FRC values obtained by plethysmography with values obtained by gas dilution methods, particularly in patients with obstructive disease. The ratio of FRCpleth/FRCN2 or FRCpleth/FRCHE can be used as an index of gas trapping. This ratio is usually near 1.0 in patients with normal lungs, or even those with a restrictive lung disorder. Values greater than 1.0 indicate gas volumes detectable by the plethysmograph but hidden to the gas dilution techniques. This ratio has been used to evaluate candidates for lung volume reduction surgery.

Some evidence suggests that in severe airway obstruction, FRC may actually be overestimated when the plethysmographic technique is used. This occurs primarily because PMOUTH (measured when the shutter is closed) may not equal alveolar pressure if the airways are severely obstructed. Rapid panting rates aggravates this inaccuracy. Care should be taken that patients with spirometric evidence of obstruction pant at a rate of 0.5 – 1 HZ.

In the above photo of our plethysmograph in our Hamilton Lab you will also see four gas cylinders two are required for our gas transfer testing and the remaining two are gases used to calibrate the analyser and cross reference for calibration.

Also note the dual computer screen which is used with the cycle ergometer which you can just see the tip of at the right of the photo. I will showcase our cardio pulmonary exercise test next month.

Vanessa

Pneumothorax

Two weekends ago I was able to talk to a conference of local GPs gathered in Warrnambool. The brief was to discuss respiratory emergencies around a scenario that involved a hypothetical bus crash. Amongst other conditions we discussed management of pneumothorax.

Management of a traumatic pneumothorax is something which I am generally very happy to leave in the hands of the surgeons. Spontaneous pneumothorax is much more in my ball-park.

Spontaneous pnemothoraces – where the surface of the lung develops a ‘blow-out’ type of air leak, and the lung – as a consequence – collapses are considered as either:
- primary (no underlying lung disease) or
- secondary (underlying lung disease)

Management is different for the two different sorts of patients. The British Thoracic Society guidelines published in 2003 are excellent. They simplify evaluation of spontaneous pneumothorax, so that we differentiate in addition to the above discriminators (primary or secondary) predominantly only on whether the pneumothorax is small (less than 2cm rim between the lung edge and the ribs) or large (more than a two centimeter rim). Once that discrimination has been made, the acute management will follow along the lines indicated in the following flow charts:

Note that conservative management is very seldom pursued if the pneumothorax is secondary.

Once the emergency management plan has been implemented, the question is whether to refer for surgical treatment – either resection of blebs on the lung surface or pleurodesis (usually done videoscopically). There is around about a 40% risk of pneumothorax after the first spontaneous pneumothorax. The following is a fair list of indicators for referral for surgical intervention / referral
- second ipsilateral (same side) pneumothorax
- first contralateral (other side) pneumothorax
- bilateral spontaneous pneumothorax
- persistent air leak once a chest tube has been inserted (>5-7 days of tube drainage, air leak persist or lung has failed to fully re-expand)
- spontaneous haemothorax
- professions at risk – eg pilots, divers – where a recurrence would be disastrous.

Andrew

What is organic-dust toxic syndrome?

Two weeks ago, for five days, the National Centre for Farmer Health, which is based in Hamilton and affiliated with Deakin University, ran a five day Agricultural Health and Medicine course.

I spoke on the first day of the course about respiratory disease affecting farmers. There were two aspects of the talk I considered to be blog-worthy.

The first is ‘Organic dust toxic syndrome’ (ODTS). This is an entity about which I was entirely naïve until I began to practice in the Western District and read about occupational hazard facing farmers.

Organic dusts are those inhalable particles that arise from grains, and also from animal dung when it is dried and crushed – for example, under foot in a stock yard on a dry day. They contain multiple potentially hazardous compounds, but perhaps the most significant (and most prevalent) is endotoxin. This fragment of gram negative bacteria is thought to be very significant in inducing immune system inflammatory response, and a key mediator of illness in life-threatening gram negative sepsis.

Farmers, grain workers, swine handlers (enclosed livestock environments are particularly hazardous) may inhale this substance. If they do, then it can act in the airways to induce an acute inflammatory response. The resultant illness – ODTS – is ‘flu like’ and, I am sure, often misdiagnosed as such. The key is that there will usually be a history of massive exposure to inhaled organic dusts; for example, a particularly dry and busy day at the stockyards or silo with a lot of dust in the air. If many workers had the same exposure then many of them will likely to be sick at the same time. It resolves, like the flu, over several days but will recur after similar repeated exposure.

A good description of ODTS, along with a comparison of the less common ‘Farmers Lung’, is found on the University of Missouri website. I am concerned that this entity is common, but often misdiagnosed as viral illness or pneumonia, and remains therefore as a hidden, significant occupational hazard for agricultural workers. Those of us who provide care to such workers – particularly GPs – need to be aware of it and ask the appropriate occupational questions.

The second thing I wanted to share was the following graph from the Sustainable Farm Families research.

This research used the Piko6 device as a sort of spirometer (it measures FEV1/FEV6 rather than FEV1 over FVC) to obtain lung function measures from farmers. If the ratio was below 75% then it was reported as 'poor' lung function. Note the discrepancy between dairy farmers and other farmers - with five to seven percent more farmers in cropping, cattle and sheep ventures having ‘low’ lung function when compared with dairy farmers. This needs to be teased out further, but does lend one to suspect that there are less respiratory toxins in dairy farms than in other farming environments in our district.

Andrew

Now practicing at our new rooms at 2/14 Crouch Street, South Mt Gambier

After some time our desire to have our own practice in Mt Gambier has reached fruition and we commence consulting and lung function testing there on Wednesday 10 March.

We identified that our patients in the Mt Gambier region were keen to have Dr Bradbeer consult on a more regular basis and in Mt Gambier. We are also keen to provide a service to our patients reflective of that which they receive in our practice at Lonsdale Street in Hamilton.

We are currently consulting and performing lung function testing on Wednesdays, from 10am to 4pm and over the next few months expect to secure the services of another physician who will also consult at the Crouch Street South practice. Further to this, we are taking steps to have a nurse in attendance for consulting; we will keep you updated on the progress of this service.

To make appointments, please continue to contact our Hamilton office on 1800 184 828. Until we increase our hours at the new practice, Crouch Street South will only be contactable by phone on Wednesdays from 10am to 4pm.

Payments can be made during our office hours on Wednesdays or posted to PO Box 573 Hamilton Vic 3300. To ensure we receive the payment please do not leave at any other location.

There are 4 car parks at the back of the premises which are clearly identified as Regional Respiratory Medicine.

If you have any questions relating to the new practice please phone us and we will gladly take your inquiry.

Maureen

Doctors advice to smokers

I was prompted to write this blog for a couple of reasons.
The first was Heather and I had been discussing the role of spirometry for all smokers over 45 years old. This can show signs of early COPD and be a powerful incentive to quit. A few years ago now I worked as a quit facilitator and in the courses a peak flow meter and norms for their age were used as a means to show smokers the damage they were doing.

The second was that in the news this week Barack Obama latest medical was made public (apparently the public has a right to this normally confidential information as the status of his health may affect the way he governs). One of the pieces of advice that has given to the leader of the USA by his doctor was to quit smoking (it was a little know fact that he smoked).

A study by the Centre for Behavioural Research in Cancer that was prepared for Quit Victoria looked at Doctors advise to their patients about smoking: 2004.

Previously research has demonstrated that advice from health professional, even during brief interventions can be effective in encouraging quitting smoking.

Since the introduction of guidelines under the five A's model (Ask, Assess, Advise, Assist and Arrange) it was reported that advice to stop smoking increased from 11% to 37% (between 1990-1998).

The 2004 report looked at the experiences of smokers and those who had recently quit who had visited the Gp in the last 12 months; whether their doctor asked about their smoking behaviours and if so whether they were given advice to quit and if on receiving this advice it was associated with attempts to quit and motivation to quit.

The results showed that 73% of Victorian adults, who were either current smokers or who had quit within the past 12 months, were asked by their GP whether they smoked. Smokers aged between 30-49 years (75%) and those who smoked 15 cigarettes or more per day were most likely to be given advice on ways to quit smoking by their GP.

Respondents were most likely to be recommended to cut down their smoking (57%) and also given information regarding the use of NRT (30%), followed by other advice (21%). Advice to call the quit line was given to only 13% of respondents.

The respondents that received advice were more motivated to quit with over half reporting they were seriously considering quitting in the next 6 months, compared with those who had not received advice.

It is evident smokers are being asked about their smoking status and that advice from a GP has a demonstrated impact on making at least one quit attempt and increased motivated to quit smoking. It will be interesting to see what impact Obama's doctors recommendation will have on his smoking status.

Jessica

Will losing weight help?

The answer is yes! And the question, is invariably raised by patients at the sleep laboratory that are having a cpap implementation study after diagnosis of obstructive sleep apnoea.

It is a terrible cycle. We know that being overweight or obese increases the chances of having OSA and that losing weight can help but losing the weight is not always that easy when excessive levels of sleepiness are in play due to the OSA (hence the cycle).

It is always fantastic when a patient returns for a repeat diagnostic sleep study to see if their AHI has decreased after a significant weight loss. Some do it over time with diet and exercise and some undergo bariatric surgery.

A study on Polysomnography before and after weight loss in obese patients with severe osa demonstrated there was a decrease in the AHI with a decrease in BMI.

The subjects in this study all had laparoscopic adjustable gastric banding (LAGB) and prior to surgery all had severe OSA. Researchers also measured daytime sleepiness, the metabolic syndrome and quality of life (QOL) pre and post. Baseline BMI was 52.7kg/m(2).

The second PSG was conducted on average of 17.7+/-10 months after surgery and mean percentage of excess loss and weight loss were 50.1+/-15% and 44.9+/-22 kg (range 18-103 kg), respectively.

The AHI fell significantly from 61.6+/-34 to 13.4+/-13, improved sleep architecture was present with increased REM and stage 3 and 4 sleep. Daytime sleepiness, measured by Epworth Sleepiness Scale, also dropped from 13+/-7.0 to 3.8+/-3.0.

Weight can be a tricky subject to deal with but whenever faced with this question by a patient with a BMI in the overweight or obese category the answer is YES losing weight will help.

Jessica

nb: I have been asked to explain what AHI stands for. It is Apnoea Hypopnea Index that is used to assess the severity of OSA. The number of apnoeas and hypopneas per night are added up and divided by the hours of sleep. This gives a per hour score. Under 5 is normal, 5-15 is mild, 15-30 is moderate and over 30 is classified as severe.

Teeth Grinding and Sleep Apnoea

I thought this might be worth sharing – we commonly associate obstructive sleep apnoea with snoring and gasping for breath. This article talks about teeth grinding in relation to this condition and should be considered when assessing sleep disorders.

Teeth grinding on its own can lead to other health problems such as headache, jaw or ear pain, aching teeth and jaws, and strain on the joints and soft tissue of the jaw. Often people are not even aware they are grinding their teeth (some partners however are).

Recent research presented at CHEST 2009 – the 75^th annual international scientific meeting of the American College of Chest Physicians highlighted a link between night time teeth grinding (bruxism) and those that suffer from Obstructive Sleep Apnoea (OSA).

Researchers focussed on the potential influence of factors such as gender, ethnicity, gastroesophageal reflux and bruxism in relation to OSA. The small retrospective study looked at 150 men and 150 women with OSA, and was made up of 50 Caucasians, 50 African-Americans, and 50 Hispanics in each group.

Overall, 25.6% of patients were teeth grinders (almost one in four), and 35% complained of gastroesophageal symptoms and heartburn at night. Results showed a higher incidence of bruxism in men than women (43% VS 31%) and when comparing ethnic groups, Caucasians demonstrated the highest rate of bruxism (35%). The highest rate of gastroeosophageal reflux was seen in the African-American study group – 40% VS 34% in Caucasians and 31% in the Hispanic population groups.

Other factors cited which are believed to link OSA and bruxism are anxiety and caffeine. We already know that OSA (untreated or poorly controlled) can lead to altered mood including depression and anxiety. Sleep deprivation can in turn lead to a high intake of caffeine which can in turn be associated with a high risk of teeth grinding.

It is the end of an apnoeic event (usually after an arousal) that sleep bruxism is often seen. I t has been suggested that as men usually have more severe OSA, and therefore more associated arousals per night that this may explain a higher percentage of men in this group suffering from teeth grinding.

Finally, some studies are suggestive of treatments such as Continuous Positive Pressure Therapy (CPAP) for OSA in helping treat and potentially eliminate the secondary health problem of nocturnal bruxism.

We regularly receive referrals at Regional Respiratory Medicine from Oral Medicine Specialists and General Dentists who recognize how one or more symptoms might be associated with other conditions such as sleep apnoea.

Lisa