Correlation of nasal symptoms with objective findings and surgical outcome measurement

Thesis submitted for the degree of Master of Surgery, University of London, 1993.
Published (excluding Chapter 9) 1996.
Recompiled HTML format June 2007
© 1993 – 2014 JW Fairley

Mr James W Fairley BSc MBBS FRCS MS
Consultant ENT Surgeon

Chapter 3
Nasal pressure probe studies using a new device in healthy volunteers: Pressure applied to middle turbinate causes pain at lower threshold than inferior turbinate or nasal septum

Chapter 3 Contents

Thesis Contents

Summary

A spring loaded device was designed and built to measure the threshold at which pressure applied to the nasal mucosa causes pain, and to investigate the hypothesis that the middle turbinate is more sensitive to pressure than other areas of the nose.

In a single blind physiological study on eight healthy male volunteers, mean age 30 years, range 24 – 35, the pressure threshold for pain was measured at three sites:

  • The anterior septum (Little’s area)
  • The medial aspect of the anterior part of the inferior turbinate
  • The inferior aspect of the anterior part of the middle turbinate.

In all subjects, the middle turbinate was the most sensitive area, in one subject equally with the inferior turbinate. Mean pain thresholds were:

Middle turbinate 109 kPa
Septum 197 kPa
Inferior turbinate 175 kPa

The differences between the middle turbinate and the other sites were significant (p = 0.0117 vs. septum, p = 0.018 vs. inferior turbinate, Wilcoxon matched pairs signed rank test, two tailed).

An instrument has been developed to measure the pressure threshold for pain in the nasal mucosa. The middle turbinate is more sensitive and results in pain at a lower pressure than the inferior turbinate or nasal septum.

This study supports the concept of mucosal pressure contact zones, particularly around the middle turbinate, as a cause of facial pain and headache.

Introduction

Greenfield Sluder in 1918 put forward the concept of mucosal contact pressure zones, particularly involving the middle turbinates and septum, as one cause of headache.

More recently Heinz Stammberger and other nasal endoscopists (Stammberger and Wolf 1988) have emphasised the importance of nasal mucosal pressure contact zones, not only as a cause of facial pain and headache, but also as the pathophysiological basis of nasal polyp formation, and stagnation of mucociliary clearance leading to subsequent infection in the sinuses.

There has been very little experimental physiological work done to measure the actual pressures involved in the mucosal contact zone phenomenon. Harold Wolff and his neurological colleagues in the 1940’s studied the pressure necessary to cause pain in the nose and sinuses (Dalessio, 1972). They also studied the somatotopic surface projections of pain resulting from electrical stimuli applied within the nasal fossa and sinuses (Ray and Wolff, 1940; Wolff, 1943). They measured pressure inside a balloon catheter, blown up in the maxillary antrum, and found that very high pressures were necessary to cause pain in the antrum. Pressure applied in the middle meatus caused pain at much lower levels. They concluded that the pain of acute maxillary sinusitis was probable mediated more by the congestion within the middle meatus than the infection in the antrum itself.

I was unable to find any published papers repeating this work, and therefore decided to carry out a further study, using modern techniques and equipment.

There were two objectives:

  1. To measure the threshold at which pressure applied to the nasal mucosa causes pain.
  2. To test the hypothesis that the middle turbinate is more sensitive to pressure than other areas of the nose.

In my early attempts to repeat the measurements performed by Wolff, I used a fine balloon catheter. The smallest available was a cardiac catheter. It was possible to place this reasonably accurately within the nasal fossa, under microscopic control. There were however two major problems. Firstly, when the balloon was inflated, at least two mucosal surfaces were compressed. For example, if the balloon was in the middle meatus, both middle turbinate and lateral nasal wall would be stimulated. If it were placed medial to the middle turbinate, both turbinate and septum would receive the stimulus. This would complicate interpretation of the results. Secondly, the relationship between the pressure measured, inside the balloon, and the pressure being exerted on the mucosa by the external surface of the balloon was found to be totally non-linear and unpredictable. This calls into question the validity of any previous work based on pressure measurements using balloon catheters. I therefore tried a new approach, and, with the help of Dr. J.C. Stevens (Medical Physicist) designed and built a mechanical pressure applicator, the Sheffield nasal pressure probe (Figure 3.1).

Methods

Apparatus

A spring loaded applicator (Figure 3.1) was designed and built to apply and measure a variable pressure to the nasal mucosa at various sites. The instrument has interchangeable plastic tips mounted at 90 degrees to a stainless steel shaft. The probe tips are made of Delrin, a plastic which is rigid, not thermoconductive (thereby avoiding any cold stimulus) and easy to machine accurately. The shaft pivots on a fulcrum incorporated into the handle, the movement being resisted by a spring. A deflection scale is incorporated in the probe handle. Thus by Hooke’s law, the deflection on the scale is proportional to the force applied. Changing to finer springs and different probe tips with alternative surface areas allows the instrument to be calibrated to a range of sensitivities. The device applies a measured variable force to a known surface area. Pressure applied is calculated by dividing the force necessary to produce a specific deflection of the lever by the surface area of the probe tip in contact with the mucosa, according to the formula:

Pressure = Force / Surface Area

Figure 3.1 The Sheffield Nasal Pressure Probe

Sheffield nasal pressure probe diagram showing interchangeable probe tips and interchangeable spring

Subjects

A group of eight healthy male volunteers from the staff of the ENT department, including myself, were tested. Mean age was 30 years, range 24 – 35.

Application of the device

In single blind method, the probe was applied in random order to the nasal septum (Little’s area) the anterior part of the inferior turbinate, and the inferior aspect of the anterior part of the middle turbinate. The pressure applied was gradually increased until the subject complained of pain, the device was then removed.

Results

Calibration

The device was calibrated by suspending a series of weights from the probe tip. A near perfect linear calibration curve (Figure 3.2) was obtained over the range 55 – 270 kPa.

Figure 3.2 Calibration curve for Sheffield Nasal Pressure Probe

Calibration curve Sheffield Nasal Pressure probe

Table 3.1 Data for Calibration (figure 3.2)

Reading 0 1 2 3 4 4.5 5.5 6 6.5 7.5 8 8.5 9.5 10 11 12 12.5 13.5 14 15
Weight (g) 50 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250

Regression eqn: Slope = 0.074 X-intercept = -3.797 R squared = 0.998

Calculation for pressure at tip of probe

The pressure in KiloPascals (kPa) is calculated using the regression equation from calibration data and knowing the surface area of the tip, according to the formula:

Pressure (kPa) = Reading – X-intercept x Conversion factor /
Calibration Slope x tip area

Where:

X-intercept = -3.797 (Calibration data Regression)
Slope = 0.074 (Calibration data Regression)
Tip area = 0.09 sq cm (Measured 3 x 3mm square)
Conversion factor = 0.0980665 (grams weight/cm sq to kPa; Geigy Scientific Tables)

Substituting:

Pressure (kPa) = (Reading + 3.797) x 0.098065 / 0.074 x 0.09

Eliminating:

Pressure (kPa) = (Reading + 3.797) x 14.64

The instrument in use

Initial studies showed that the device was simple, reliable and rapid in operation. The pain induced was quite severe and acute, especially when applied to the middle turbinate. Although it was difficult to persuade volunteers to have the experience on multiple occasions, repeatable measures of pain thresholds could be obtained.

Middle turbinate versus septum and inferior turbinate

In all subjects, the middle turbinate was the most sensitive area, in one subject equally with the inferior turbinate (Table 3.2).

Table 3.2
Pressure thresholds for pain at three sites in
the nose: Septum, Middle turbinate (MT) and Inferior turbinate (IT)
Raw meter reading (rdg) in Arbitrary Units. Calculated pressure(kPa)

Subject Age Septum IT MT
    rdg kPa rdg kPa rdg kPa
SRE 30 17 305 15 275 5 129
LHD 33 3 100 13 246 0 56
JWF 35 7 158 5 129 3 100
MY 31 8 173 2 85 1 70
ROB 30 15 275 10 202 10 202
MV 24 12 231 8 173 5 129
DT 27 7 158 10 202 5 129
AJP 33 8 173 2 85 0 56
Mean 30   197   175   109
S.D. 3.5   68   71   49

Mean pain threshold for the middle turbinate was 109 kPa, compared with 197 kPa on the septum and 175 kPa on the inferior turbinate.

Subjectively, the pain induced by pressure on the middle turbinate was more severe than the other sites, and was associated with lacrimation on the same side as the stimulus.

The differences in pressure thresholds between the middle turbinate and the other sites were significant (p = 0.0117 vs. septum, p = 0.018 vs. inferior turbinate, Wilcoxon matched pairs signed rank test, two tailed).

Discussion

Using a specially designed new device, the pressures required to induce acute pain when applied to the nasal mucosa were measured. The middle turbinate was more sensitive to pressure than other sites in the nose; a more severe pain was induced by approximately half the strength of the stimulus.

The pressures concerned are in fact very high, greater by a factor of ten than the pressures that could be generated physiologically by vasomotor changes. Clearly the maximum that could be sustained long term would be systolic blood pressure, around 10 kiloPascals, otherwise the mucosa would necrose.

On the other hand, the artificial pain generated by the probe is quite severe and acute. It has been quite difficult to get volunteers for the repeat measurements! It is likely that if lower pressures were applied for a longer period, a less acute type of pain would be induced, more akin to the discomfort, pressure headache symptom commonly complained of by patients. This type of stimulus could not be maintained easily by the apparatus. A soft-walled balloon might be more suitable, but there are other difficulties with this approach (see introduction).

An alternative strategy would be passive monitoring of pressure by a wafer-thin transducer placed between two adjacent mucosal surfaces. No such transducer is currently available. It might be possible to have one custom built (S. Johnson, Gaeltec Ltd, Isle of Skye, personal communication). The prototype equipment would cost around £1,000, which was not available at the time of this study.

Conclusions

An instrument has been developed to measure the pressure threshold for pain in the nasal mucosa.

Using this device it has been shown that the middle turbinate is more sensitive and results in pain at a lower pressure than the inferior turbinate or nasal septum.

Although the pressures involved are higher than those which would be generated physiologically, this study provides some experimental support for the concept of mucosal pressure contact zones, particularly around the middle turbinate, as a cause of facial pain and headache.